Research Radartracking 11 published studies · 7 human · 9 clinical trials · 13 cancer pages · updated Jun 2026Open the Research Map →
Risk factor

Tobacco smoke

The strongest established carcinogen exposure for several cancers.

Educational only. This page reports what published guidelines and studies describe. It is not medical advice and is not a claim that tobacco smoke treats, prevents, or cures cancer. Decisions are yours and your care team's.

What the studies report: a cited, human-reviewed summary, kept current as the evidence changes and retracted findings are removed.

Reviewed Jun 2026 · OncoForge editorial · How we review →

Evidence at a glanceNo graded study evidence yet
423 source documents in the Tobacco smoke corpus

last checked June 9, 2026

Key points

  • Overview: Tobacco smoke is described in the sources as a carcinogenic exposure and a population-level risk factor associated with several cancers, especially lung cancer. The evidence base is mainly observational and often summarized in systematic reviews and meta-analyses.

6 sections — tap any heading to expand its cited detail. Key points are above.

OverviewTobacco smoke is described in the sources as a carcinogenic exposure and a population-level risk factor associated with several cancers, especially lung cancer. The evidence base is mainly observational and often summarized in systematic reviews and meta-analyses.24 points
  • Sources describe cigarette smoking as a risk factor or associated exposure for vulvar cancer, small cell lung cancer, oral and pharyngeal cancer, gastric cancer, early-onset colorectal neoplasms, and possibly esophageal squamous cell carcinoma; the prostate cancer source reports mixed or inverse associations rather than identifying smoking as a risk factor. [1][2][3][4][5][6][7][8]
  • Tobacco smoke is described in the sources as a carcinogenic exposure, and one source notes that smoking is the main risk factor for lung cancer. [9][10]
  • Sources describe cigarette smoking as a combustible tobacco exposure linked to several cancer sites, including nasopharyngeal cancer, bladder cancer, oral squamous cell carcinoma, and upper gastrointestinal cancers. [11][12][13][14]
  • Sources describe waterpipe smoking as being associated in observational evidence with several outcomes, including gastric, lung, bladder, and esophageal cancers and cancer mortality; another source reports tobacco smoking was associated with esophageal adenocarcinoma. [15][16]
  • The evidence base in the sources is mainly observational and summarized in systematic reviews and meta-analyses. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]
  • Sources describe cigarette smoking as being associated with substantial smoking-attributable mortality and report tobacco use prevalence across multiple cancer types among cancer patients. [32][33]
  • Tobacco smoke is described in the sources as a cancer-related exposure, with evidence reported for several cancer outcomes and treatment-related outcomes. [34][35][36][37]
  • Tobacco smoke is described in the sources as a mixture of thousands of chemical compounds generated from tobacco burning. [38][39][40]
  • The sources state that tobacco smoke is classified by IARC as carcinogenic for lung tissues. [41]
  • Tobacco smoke is described in the sources as a cause of lung cancer and as a source of thousands of compounds, including many carcinogens. [39][40]
  • The sources also describe smoking as a risk factor for several other cancers and for second primary cancers in cancer survivors. [39][42]
  • Sources describe cigarette smoking as a risk factor for bladder cancer, secondhand smoke as associated with oral cancer, and esophageal cancer risk models as commonly including cigarette smoking as a predictor. [43][44][45]
  • The sources describe cigarette smoking as a recognized risk factor for pancreatic cancer, and one source says active cigarette smoking was labelled as a carcinogenic factor for 12 cancers in an IARC report. [46][47]
  • The sources describe a well-documented association between tobacco smoking and lung cancer risk, and one review states that tobacco exposure is the most significant risk factor for lung cancer. [48]
  • Sources describe smoking as a risk factor for lung cancer, heavy cigarette smoking as associated with renal cell carcinoma incidence and mortality, smoking as one of the main risk factors for gastric cancer, and tobacco smoking as a main risk factor for bladder cancer. [49][50][51][52]
  • Several observational meta-analyses in the sources evaluate cigarette or tobacco smoking in relation to cancer or precancer risk, and some report increased risks. [20][21][22][23]
  • The sources describe tobacco smoke exposure as cigarette smoking or tobacco smoking. [24][26]
  • The sources describe cigarette smoking in relation to lung cancer and state that eliminating tobacco smoking is the best strategy to prevent lung cancer. [53][54]
  • The sources also describe tobacco smoking as a historical behavioral risk factor for oral cancer and as a cause of smoking-related changes in gene methylation in non-small cell lung cancer. [55][53]
  • Tobacco smoke is described in the sources as a cigarette-smoking exposure that is linked to cancer risk or cancer outcomes in several cancer types studied in meta-analyses. [27][28][29][30][31]
  • The sources describe tobacco smoke as associated with increased breast cancer risk in some studies, and also as a risk factor for bladder cancer and lung cancer. [56][57][58]
  • Tobacco smoke is an exposure that people can encounter through cigarette smoking and waterpipe tobacco smoking. [59][60]
  • The sources describe tobacco smoke, especially cigarette smoking, as a population-level risk factor associated with several cancers. [61][62][63][64][65][66]
  • One source states that the 2004 IARC Monograph on Tobacco Smoke and Involuntary Smoking recognized 13 cancer sites related to tobacco smoking. [61]
How people are exposedThe sources describe tobacco-smoke exposure mainly through cigarette smoking, with common measures including current, former, ever, and heavy smoking, as well as smoking duration, intensity, pack-years, and time since quitting. They also mention exposure through waterpipe smoking, other combustible tobacco use, and secondhand smoke.35 points
  • Exposure is described mainly as cigarette smoking, current smoking, former smoking, ever smoking, smoking frequency, smoking duration, and time since quitting. [3][67][4][2]
  • Smoking metrics included cigarettes-per-day, smoking duration, pack-years, square-root pack-years, logcig-years, the comprehensive smoking index, age-of-initiation, and years-since-quit. [67]
  • Exposure to tobacco smoke occurs through cigarette smoking and through secondhand smoke exposure. [10]
  • The sources describe exposure through cigarette smoking and other inhalational exposures, including waterpipe smoking. [11][12][13]
  • Combustible tobacco use is smoking, and smoking is described as the leading preventable cause of disease and death worldwide. [68]
  • The sources describe exposure through smoking tobacco, including cigarette smoking and waterpipe smoking; one source contrasts cigarette smoking with oral smokeless tobacco by noting the lack of pulmonary exposure with oral products. [17][15]
  • Waterpipe smoking is reported as a worldwide exposure that has increased over time and is prevalent in multiple regions, with the highest prevalence in the Eastern Mediterranean and European regions. [15]
  • The umbrella review describes cigarette smoking as the highest-risk combusted tobacco exposure compared with smoke-free tobacco products, while still identifying cigarette smoke as the source of major health risks. [17]
  • Exposure is described as active cigarette smoking, and one source also mentions secondhand smoke exposure. [32][69][70][33]
  • The review reported cigarette smoking and other tobacco-use categories, including waterpipe, Naas, and pipe. [33]
  • Exposure is described as cigarette smoking, former smoking, and waterpipe smoking. [34][71][37]
  • In the Middle East meta-analysis, the pooled prevalence of current cigarette smoking was 17.41% and the pooled prevalence of current waterpipe smoking was 6.92%. [71]
  • People are exposed to tobacco smoke by smoking tobacco products, and the sources also mention second-hand tobacco smoke as an exposure. [38][41]
  • One source notes that cigar products generate smoke with a composition similar to cigarettes and, for some toxicants, greater levels. [72]
  • Exposure is described as active cigarette smoking, former smoking, or smoking status categories such as current smoker, ex-smoker, former smoker, never-smoker, and non-smoker. [6][8]
  • One source explicitly excludes passive smoking from its study population. [6]
  • Exposure is discussed through cigarette smoking, waterpipe smoking, and smoking history measured in pack-years or lifetime smoking liability. [73][40][39]
  • Waterpipe smoking is described as rising globally and as influenced by flavors, marketing, social use, and misperceptions that it is less harmful or addictive than cigarettes. [73]
  • Exposure to tobacco smoke is described as cigarette smoking, including smoking intensity, pack-years, smoking duration, and secondhand smoke inhalation. [43][44][74]
  • The sources describe cigarette smoking, including current, former, and heavy smoking categories, and one review discusses smoking reduction measured by cigarettes per day. [47][75]
  • One review notes that cigarette smoke exposure can temporarily affect thyroid hormone levels and that the association with thyroid cancer was not seen in people who had quit smoking. [47]
  • Exposure is described as cigarette smoking, including current smoking, former smoking, smoking intensity, smoking duration, and time since quitting; a separate cited review discusses e-cigarettes in head and neck cancers. [76][77][48]
  • One review notes that smoking behavior data can be used in lung cancer projection methods, including smoking variables and smoking-attributable fractions. [48]
  • Exposure to tobacco smoke is described as inhalation exposure to tobacco smoke carcinogens and as smoking status categories such as current smoker, former smoker, ex-smoker, and non-smoker. [23][22]
  • One source also evaluates smoking cessation by time since quitting, including 5 or more years, 10 or more years, and 20 or more years after cessation. [22]
  • In the cited studies, exposure occurred through smoking cigarettes or tobacco products, and some analyses also used pack-years, smoking status, and age at smoking onset to describe exposure. [24][26]
  • One source defined a pack-year as smoking 20 cigarettes per day for 1 year. [26]
  • The sources discuss exposure as active cigarette smoking, passive smoking, and current exclusive cigar smoking. [78][79]
  • One meta-analysis notes that the association between coffee drinking and lung cancer can be confounded by tobacco smoking, showing that smoking status can affect exposure-outcome analyses. [80]
  • The exposure assessed in the sources is cigarette smoking or tobacco smoking, usually compared with never-smokers, former smokers, or non-smokers. [27][28][29][30][31]
  • The sources describe exposure as active or pre-diagnosis cigarette smoking, smoking status, cigarettes per day, years of smoking, and pack-years. [56][81]
  • One source also notes that cigarette smoking is a risk factor for both diabetes and bladder cancer, making it a potential confounder in studies of bladder cancer. [57]
  • One source describes exposure as cigarette consumption measured by current smoking, ever smoking, ex-smoking, cigarettes per day, and years of smoking. [59]
  • Another source describes exposure as waterpipe tobacco smoking, including smoking waterpipe in groups. [60]
  • The exposure described in the sources is cigarette smoking, including current smoking, former smoking, smoking duration, cigarettes per day, pack-years, and age at smoking initiation. [65][66][62][64][63][61]
Evidence of cancer riskTobacco smoke is linked to increased risk for many cancers, with especially strong evidence for lung, oral and pharyngeal, nasopharyngeal, bladder, gastric, esophageal, cervical, and colorectal cancers. Several sources also report dose-response patterns, with risk generally rising with smoking intensity or duration and falling after quitting.71 points
  • Nearly all cases of small cell lung cancer are attributable to cigarette smoking, and smoking is the best established environmental hazard of lung cancer, accounting for 80% of the worldwide lung cancer burden in males and at least 50% in females. [2][26]
  • A 2024 NCCN guideline lists cigarette smoking among the known risk factors for vulvar cancer. [1]
  • The same meta-analysis reported a non-linear dose-response pattern in which oral and pharyngeal cancer risk increased with smoking intensity and duration and declined with time since quitting. [3]
  • A dose-response meta-analysis of oral cancer reported a peak relative risk of 5.98 at 30 smoking units per day and a peak relative risk of 2.19 at 40 years of smoking duration. [4]
  • One source states that the excess lung cancer risk among continuous smokers relative to never-smokers is in the order of 20- to 50-fold. [10]
  • Tobacco smoke contains harmful and carcinogenic compounds and can cross the placental barrier during pregnancy. [9]
  • A systematic review of 18 studies found no consistent evidence of an association between maternal tobacco smoking during pregnancy and childhood brain tumors. [9]
  • A 2025 meta-analysis reported that cigarette smoking was associated with higher nasopharyngeal cancer risk compared with never smoking, with pooled relative risks of 1.61 for current smokers, 1.28 for former smokers, and 1.62 for ever smokers. [11]
  • The same meta-analysis reported that nasopharyngeal cancer risk increased linearly with smoking intensity and duration and decreased linearly with time since quitting. [11]
  • A 2025 meta-analysis of studies on gastroesophageal disease reported mixed findings for smoking, including one study with no significant association with gastroesophageal reflux disease and other studies reporting positive associations with reflux disease, Barrett’s esophagus, and peptic ulcer disease. [13]
  • In that gastroesophageal review, current tobacco use was reported as a significant risk factor for reflux esophagitis, Barrett’s esophagus, and peptic ulcer disease in one cross-sectional study, while associations with esophageal squamous cell carcinoma and gastric cancer were not significant in that study. [13]
  • A 2025 systematic review of oral squamous cell cancer reported that developing oral squamous cell carcinoma was mostly associated with combustible cigarettes and to a lesser extent with e-cigarettes. [14]
  • A 2025 bibliometric analysis stated that tobacco smoking remains the most significant modifiable contributor to bladder cancer and cited reports of a two- to fourfold increased risk compared with people who do not smoke. [12]
  • A 2025 systematic review of vaping and lung cancer reported that four of five included observational studies found positive associations between e-cigarette use and lung cancer risk, while one study found no significant relationship after adjustment. [82]
  • One review reports consistently large relative risks for cigarette smoking and lung cancer and higher risks for COPD, mouth cancer, and heart diseases than for certain oral smokeless tobacco products; another states that tobacco smoking is an important risk factor and potentially a major confounding factor in occupational lung cancer studies. [17][83]
  • The Korean meta-analysis reported elevated pooled hazard ratios for current smokers versus non-smokers for overall cancer and, among men, for esophageal cancer, lung cancer, stroke, atherosclerosis, COPD, and pneumonia; among women, it reported higher HRs for cancer overall and for cancers of the esophagus, larynx, lung, and bladder, IHD, atherosclerosis, COPD, and pneumonia. [32]
  • A 2024 meta-analysis of colorectal cancer in Africa reported that tobacco consumption was associated with higher odds of colorectal cancer, with a pooled odds ratio of 2.27. [70]
  • A 2024 meta-analysis of gastric cancer reported that current smokers had a pooled relative risk of 1.53 compared with never smokers and former smokers had a pooled relative risk of 1.30 compared with never smokers. [69]
  • That gastric cancer meta-analysis reported that risk increased with smoking intensity up to 20 cigarettes per day and increased linearly with smoking duration, while risk decreased linearly with time since quitting. [69]
  • A 2024 meta-analysis of head and neck cancer reported that former smokers had a lower relative risk than current smokers, with a pooled relative risk of 0.40. [84]
  • In that head and neck cancer meta-analysis, the relative risk decreased from 0.67 for people who had quit for less than 5 years to 0.20 for people who had quit for more than 20 years. [84]
  • A 2023 meta-analysis reported that current cigarette smoking was associated with higher relative risks of invasive cervical cancer and preinvasive cervical lesions compared with never smoking, and that former smokers also had higher relative risks than never smokers for both outcomes. [35]
  • In that meta-analysis, the relative risk of cervical cancer increased with smoking intensity and decreased with time since quitting, reaching the level of never smokers about 15 years after quitting. [35]
  • A meta-analysis in Middle Eastern countries reported that the highest population attributable risk for cigarette smoking was for oesophageal (35.0%), lung (30.50%), and gastric (8.20%) cancers. [71]
  • A 2024 meta-analysis reported reduced melanoma risk among current smokers compared with never-smokers. [34]
  • A 2024 systematic review reported that tobacco smoking was associated with worse radiotherapy-related outcomes, including more second primary cancers, lower median overall survival, more infections, more fatigue, more pain, poorer cognitive function, more speech disturbances, higher metastasis risk, higher locoregional recurrence risk, oral mucositis, severe acute radiation skin reactions, and myocardial infarction. [37]
  • A 2023 meta-analysis states that cigarette smoking is the leading risk factor for early death and that smoking causes carcinogenesis, and it reports that incidence of lung squamous carcinoma is significantly increased by cigarette smoking. [38]
  • A 2023 systematic review of bladder cancer risk factors states that tobacco smoking is among the most substantial and most established risk factors for bladder cancer. [85]
  • A 2023 systematic review and meta-analysis of female breast cancer reports pooled relative risks of 1.07 for current smokers, 1.08 for former smokers, and 1.09 for ever smokers versus never smokers. [86]
  • The breast cancer meta-analysis reports that the association differed by menopausal status, with pooled relative risks of 1.03 in premenopausal women and 1.13 in postmenopausal women for current smokers versus never smokers. [86]
  • The arsenic-smoking systematic review says the contribution of arsenic and its compounds to the carcinogenic effects of other agents, such as tobacco smoke, is not well characterized. [41]
  • In a 2023 systematic review and meta-analysis of six studies on early-onset colorectal neoplasms, current smoking was associated with higher odds compared with non-smoking (OR 1.33, 95% CI 1.17 to 1.52; P < 0.0001; n = 95,406), while former smoking was not significantly associated with early-onset colorectal neoplasms (OR 1.00, 95% CI 0.86 to 1.18; P = 0.97). [6]
  • The colorectal meta-analysis reports a positive association for current smoking in case-control studies and cross-sectional studies, but not for former smoking in either study type, and a positive association for current smoking in studies from Asia, but not in studies from America and Europe. [6]
  • The prostate cancer meta-analysis reports an increased risk estimate for ever smoking in the pre-PSA screening era, but no association in North America, Europe, and Australia overall. [8]
  • A Mendelian randomization meta-analysis reported that genetic liability to smoking initiation and to lifetime smoking was associated with increased risk of lung cancer and several other site-specific cancers, and that the findings support a causal effect of cigarette smoking in a wide range of diseases, including several cancers. [39]
  • A systematic review of second primary cancers found higher pooled risk for smoking-related second primary cancers among former smokers and current smokers compared with never smokers. [42]
  • A 2022 dose-response meta-analysis found a non-linear positive dose-response relationship between cigarette smoking and bladder cancer risk across 8 cohort studies and 44 case-control studies, and the relationship plateaued only when smoking intensity reached 20 cigarettes per day. [43]
  • A 2021 meta-analysis of three cohorts found that tobacco smoking was a significant risk factor for second primary lung cancer among people with an initial primary lung cancer, and that smoking pack-years, smoking intensity, and meeting USPSTF lung cancer screening criteria were each associated with increased second primary lung cancer risk in pooled analyses. [74]
  • The same study reported that smoking cessation after an initial primary lung cancer diagnosis was associated with a lower second primary lung cancer risk in a small subset analysis. [74]
  • A 2021 systematic review of esophageal cancer prediction models found that cigarette smoking was included in all esophageal squamous cell carcinoma models and all esophageal adenocarcinoma models reviewed. [45]
  • A 2021 meta-analysis of 23 studies reported an overall odds ratio of 0.798 for thyroid cancer among smokers versus non-smokers, but the authors interpreted the finding cautiously because the studies were observational and heterogeneous. [47]
  • In that thyroid-cancer meta-analysis, case-control studies showed an odds ratio of 0.779, while two prospective cohorts showed a relative risk of 1.090 with a confidence interval that included 1. [47]
  • The same smoking-reduction meta-analysis did not find a significant difference for all-cause mortality, all-cancer risks, or smoking-/tobacco-related cancer risk among people who reduced smoking. [75]
  • A review of primary melanoma of the lung reported that about one third of cases with available smoking data were active smokers, about one fifth were ex-smokers, and about 45% were never smokers. [87]
  • A 2019 meta-analysis reported pooled relative risks for kidney cancer of 1.39 for current smokers and 1.20 for former smokers compared with never smokers, and risk increased with smoking intensity and duration and decreased with time since quitting. [76]
  • A 2019 meta-analysis found no clear increase in overall ovarian cancer risk for current smokers versus never smokers, but it found a higher risk for mucinous ovarian cancer and lower relative risks for clear cell and endometrioid ovarian cancer among current smokers versus never smokers. [88]
  • A 2019 systematic review of e-cigarettes and head and neck cancers found mostly laboratory-based, low-level evidence and said more longitudinal and controlled studies are needed. [77]
  • A meta-analysis of serrated colorectal polyps reported that tobacco smoking was associated with higher risk when the highest and lowest exposure categories were compared. [21]
  • A meta-analysis of lung cancer biomarkers reported that bronchial DNA adducts were associated with higher lung cancer risk compared with controls. [23]
  • A meta-analysis of esophageal cancer reported that current smoking was associated with higher risk than nonsmoking for both esophageal squamous cell carcinoma and esophageal adenocarcinoma. [22]
  • A 2016 meta-analysis reported cigarette smoking as a potential risk factor for selected neuroendocrine neoplasms, with smokers versus never-smokers showing OR 1.34 for pancreas and OR 1.59 for small intestine. [25]
  • A 2016 meta-analysis of prospective studies reported that fruit and vegetable intake was inversely associated with lung cancer risk, and it noted that the association was marginally significant in current smokers but not significant in former or never smokers. [54]
  • A 2016 meta-analysis found that when smoking was not controlled for, coffee drinking was associated with a higher pooled lung cancer risk, but among non-smokers coffee was not associated with lung cancer risk. [80]
  • A meta-analysis of non-small cell lung cancer studies reported significant associations between cigarette smoking and hypermethylation of CDKN2A, RASSF1, MGMT, RARB, DAPK, WIF1, and FHIT, and no statistical association for CDH13, RUNX3, SFRP1, MLH1, APC, PTEN, and CDH1 methylation. [53]
  • A systematic review of cigar smoking reported that IARC had previously concluded in 2004 that cigar and/or pipe smoking is causally connected to cancers of the lung and upper aerodigestive tract, including the oral cavity, oropharynx, hypopharynx, larynx, and esophagus, and causally associated with cancers of the pancreas, stomach, and urinary bladder. [79]
  • A 2014 meta-analysis reported that cigarette smoking was the best-established risk factor for urothelial carcinoma, and it found that smoking was associated with less favorable outcomes in urothelial carcinoma patients in many studies. [30]
  • In a 2014 meta-analysis of 9,975 breast cancer survivors, current smoking was associated with higher recurrence, breast cancer mortality, and all-cause mortality compared with never smoking, and former smokers with 20 to less than 34.9 pack-years and with 35 or more pack-years had higher recurrence and mortality risks than never smokers, while former smokers with less than 20 pack-years had no increased risk of any outcome. [27]
  • A 2014 meta-analysis of 31 studies found that ever-smoking was associated with lower thyroid cancer risk overall, but the authors noted strong heterogeneity and that the inverse association was seen only in current smokers and in case-control studies. [28]
  • A 2014 meta-analysis of 47 studies found that current smoking was associated with higher lung cancer susceptibility in men than in women among current smokers. [29]
  • A 2014 meta-analysis of 32 articles found a weak and non-statistically significant association between smoking and intestinal metaplasia, and concluded that the evidence did not confirm smoking as an independent risk factor for intestinal metaplasia. [31]
  • In that meta-analysis, women who initiated smoking before first birth had a stronger association with breast cancer risk, with a summary hazard ratio of 1.21 (95% CI 1.14 to 1.28). [56]
  • A 2013 meta-analysis of cohort studies reported a borderline statistically significant association between diabetes mellitus and bladder cancer risk, with an overall relative risk of 1.11 (95% CI 1.00 to 1.23), and studies that controlled for cigarette smoking reported a pooled relative risk of 1.32 (95% CI 1.18 to 1.49). [57]
  • A meta-analysis found higher relative risks of esophageal and gastric cardia adenocarcinoma among smokers compared with never-smokers, with pooled relative risks of 1.76 for ever-smokers, 2.32 for current smokers, and 1.62 for ex-smokers, and a direct association with dose and duration. [59]
  • The same meta-analysis reported a relative risk of 2.48 for at least 20 cigarettes per day and 2.32 for at least 40 years of cigarette consumption. [59]
  • A systematic review found waterpipe tobacco smoking was significantly associated with lung cancer, with an odds ratio of 2.12, and rated the quality of evidence for its outcomes as very low to low. [60]
  • A 2008 meta-analysis found that ever smokers had a pooled relative risk of 1.18 for colorectal cancer incidence versus never smokers and 1.25 for colorectal cancer mortality versus never smokers. [62]
  • A 2009 meta-analysis of prospective studies found that current smokers had a relative risk of 1.20 for colorectal cancer incidence versus never smokers, former smokers also had a higher risk than never smokers, and dose-related associations were reported for cigarettes per day, years of smoking, and pack-years. [66]
  • A 2009 meta-analysis of prospective studies reported that current smokers had increased colorectal cancer incidence and mortality, and that all four dose-response variables examined were significantly associated with colorectal cancer incidence. [65]
  • A 2008 meta-analysis found that smoking was significantly associated with colorectal cancer incidence and mortality, with stronger associations for rectal cancer than for colon cancer. [62]
  • A 2008 meta-analysis reported that current smokers had a relative risk of 1.51 for liver cancer compared with never smokers, while former smokers had a relative risk of 1.12 with a confidence interval that included 1. [63]
  • A 2008 meta-analysis of cohort studies on gastric cancer reported higher risks for current smokers than never smokers, with summary relative risks of 1.62 in males and 1.20 in females, and a trend of higher risk with greater cigarette consumption and associations with both cardia and non-cardia gastric cancers. [64]
Who is most at riskThe sources mostly do not identify a single general-population subgroup at highest risk for tobacco-smoke-related cancer outcomes, but several cancer-specific analyses report stronger associations in particular subgroups. These include differences by smoking status, sex, age, duration or intensity of smoking, and study or region categories.29 points
  • The sources identify people living with HIV as a group in whom anal carcinoma incidence is elevated, and one guideline notes that a low CD4+ T-lymphocyte nadir or prolonged severe immunodeficiency further increases risk of anal carcinoma. [89]
  • The sources report stronger or clearer associations in some subgroups and outcomes, including current smokers, ever smokers, heavier smokers, and longer-duration smokers. [11][13]
  • For nasopharyngeal cancer, the meta-analysis reported a higher pooled risk for squamous cell nasopharyngeal cancer than for undifferentiated nasopharyngeal cancer. [11]
  • The waterpipe meta-analysis reports that waterpipe smoking has become prevalent among young adults, and also among women and older adults, although the latter findings were mainly from nonrepresentative samples. [15]
  • The Korean meta-analysis reported higher smoking-attributable mortality in men than in women. [32]
  • The gastric cancer meta-analysis reported stronger associations for gastric cardia cancer than for distal stomach cancer among current smokers versus never smokers. [69]
  • The Middle East meta-analysis reported that current cigarette and waterpipe smoking were both more common in men than in women. [71]
  • The breast cancer meta-analysis reports that the pooled relative risk for current smokers versus never smokers was higher in cohort studies than in case-control studies. [86]
  • The colorectal meta-analysis reports that the positive association for current smoking was seen in both case-control and cross-sectional studies and in studies from Asia. [6]
  • The prostate cancer meta-analysis reports that the inverse association for current smoking was seen across studies from North America, Europe, Asia, and Australia, and in analyses restricted to studies with quality scores of 6 or at least 7. [8]
  • The sources identify cancer survivors as a population in which smoking-related second primary cancers and smoking relapse are important concerns. [42][90]
  • The relapse review reports that relapse rates after quitting at cancer diagnosis varied widely across studies, from 5.1% to 57%. [90]
  • The relapse review reports that younger age, higher addiction levels, male sex, lower education, lower readiness to quit, and depression were associated with higher relapse rates in some studies. [90]
  • In a review of post-radiotherapy bronchiolitis obliterans organizing pneumonia, increasing age, cigarette smoking, and increasing central lung distance were listed as risk factors. [91]
  • The kidney cancer meta-analysis reported that the risk increase was seen for both current and former smokers compared with never smokers. [76]
  • The lung cancer projection review states that smoking behavior is an important predictor for lung cancer incidence and mortality projections. [48]
  • The esophageal cancer meta-analysis reported that the reduction in risk after smoking cessation was stronger in Western populations than in Asian populations for esophageal squamous cell carcinoma. [22]
  • The bladder cancer meta-analysis reported a stronger inverse association between parity and bladder cancer risk among women who never smoked than among women who ever smoked. [20]
  • The nasopharyngeal carcinoma meta-analysis included studies from China, the USA, Southeast Asia, Europe, India, Turkey, Thailand, Malaysia, Hong Kong, and North Africa. [24]
  • The sources indicate that current smokers are the subgroup in which the fruit-and-vegetable association with lung cancer was marginally significant. [54]
  • The cigar-smoking review notes that secondary cigar smokers may differ from primary cigar smokers because they are about twice as likely to report inhaling cigar smoke. [79]
  • The breast cancer meta-analysis reported dose-dependent associations, with higher pack-year exposure linked to higher recurrence and mortality risks. [27]
  • The urothelial carcinoma review reported that findings on gender-specific effects of smoking on prognosis were contradictory. [30]
  • The thyroid cancer meta-analysis reported that the inverse association was seen only in current smokers and not in former smokers. [28]
  • The breast-cancer meta-analysis reported a higher risk signal for women who initiated smoking before menarche or after menarche but at least 11 years before first birth. [56]
  • The bladder-cancer meta-analysis found that the association with diabetes and bladder cancer was more significant in studies from Asia than in studies from Europe or the USA. [57]
  • The lung-cancer review reported a higher pooled risk among professional drivers with 10 years or more of employment than among those with shorter employment. [58]
  • In the colorectal cancer meta-analysis, the association was reported to be higher for men than for women and higher for rectal cancers than for colonic cancers. [66]
  • In the 2008 meta-analysis of tobacco smoking and cancer, the highest relative risks for current smokers were reported for lung, laryngeal, and pharyngeal cancers, followed by upper digestive tract and oral cancers. [61]
Reducing exposureThe sources consistently emphasize smoking cessation and remaining abstinent as the main way to reduce tobacco-smoke-related cancer risk. Several reviews and meta-analyses also report that risk generally declines with longer time since quitting, while some sources address cessation support or related prevention measures.22 points
  • Smoking cessation should be strongly promoted, and former smokers should be strongly encouraged to remain abstinent; patients who smoke have increased toxicity during treatment and shorter survival. [2]
  • Risk declined with time since quitting smoking in oral and pharyngeal cancer, nasopharyngeal cancer, head and neck cancer, gastric cancer, kidney cancer, and esophageal squamous cell carcinoma; one source reports a 50% reduction within 10 years for oral cavity and pharyngeal cancer, and another reports the lowest estimate after more than 20 years for esophageal squamous cell carcinoma. [3][11][84][69][76][22]
  • One source notes that public health campaigns are needed to educate people about the causes of lung cancer and increase empathy for people with a lung cancer diagnosis. [92]
  • Sources describe oral nicotine pouches as having limited evidence for cessation or reduction of cigarette use, with very low-certainty evidence in some comparisons. [68]
  • Sources describe switching completely from cigarettes to lower-risk smoke-free tobacco products as a way that may reduce health risks associated with tobacco use. [17]
  • For adults who smoke and are unable or unwilling to quit all tobacco, switching from cigarettes to lower-risk smoke-free tobacco products may reduce health risks, but this statement is about smoke-free products rather than tobacco smoke itself. [17]
  • Healthcare providers should record smoking histories, and cancer patients should undertake comprehensive smoking cessation programs. [37]
  • Prevention programmes are needed as a top priority for health interventions. [71]
  • Ongoing research to identify avoidable risk factors could reduce the number of people who get bladder cancer. [85]
  • The FDA announced intentions to propose a policy to ban flavors in cigars and later committed to propose product standards banning menthol and other flavors. [72]
  • The waterpipe cessation review found low-certainty evidence that intensive face-to-face behavioral interventions increased waterpipe quit rates compared with brief behavioral intervention, usual care, or no intervention. [73]
  • Smoking cessation interventions after cancer diagnosis included behavioral therapy, pharmacotherapy such as nicotine replacement, and mixed protocols, but most studies did not measure the utility of the interventions directly. [90]
  • In one randomized study, there was no difference in relapse rates between a brief counseling plus pharmacotherapy group and a group receiving additional relapse-prevention materials. [90]
  • Smoking cessation after diagnosis was associated with lower second primary lung cancer risk in a small subset analysis. [74]
  • Complete cessation remains the most effective approach for cancer and cardiovascular disease prevention, and the magnitude of lung cancer risk remains high among smokers. [75]
  • Sources describe smoking cessation programs as helping educate patients about their risks when undergoing radiotherapy. [93]
  • One meta-analysis reported lower esophageal squamous cell carcinoma risk among former smokers than among current smokers, with lower risk ratios after longer time since smoking cessation. [22]
  • The lung cancer biomarker meta-analysis reported that bronchial adduct levels were higher in smokers than in non-smokers. [23]
  • One meta-analysis states that eliminating tobacco smoking is the best strategy to prevent lung cancer. [54]
  • Tobacco smoking can confound associations between coffee drinking and lung cancer, so controlling for smoking is part of reducing exposure-related bias in studies. [80]
  • There was evidence for a beneficial effect of smoking cessation on prognosis in urothelial carcinoma, and smoking cessation may mitigate less favorable outcomes. [30]
  • In the NHL meta-analysis, a greater interval from quitting cigarette smoking to diagnosis was associated with better overall survival among former smokers, with an HR of 0.87 per 5 years of quitting. [81]
What we don't know yetSeveral sources note that the evidence base for tobacco smoke and cancer is limited by heterogeneity, inconsistent findings, or incomplete reporting. Some reviews also say that specific exposure types, subgroups, or post-diagnosis questions still need further study.34 points
  • The oral and pharyngeal cancer meta-analysis reports substantial heterogeneity and evidence of publication bias for former and ever smokers. [3]
  • The NSCLC meta-analysis notes that smoking metrics developed for risk prediction had not been systematically evaluated for survival outcomes before that study. [67]
  • The provided sources do not give a pooled estimate for secondhand smoke or other specific tobacco-smoke exposure levels in relation to cancer risk. [10]
  • For waterpipe smoking, the meta-analysis reports very low certainty for most cancer outcomes, indicating that the evidence remains limited despite positive associations. [15]
  • The gallbladder cancer review mentions tobacco smoking among significant associations with lower credibility, but the excerpt provided here does not give a specific pooled estimate for smoking. [19]
  • The Korean meta-analysis notes heterogeneity in some pooled hazard ratios and says this may reflect differences in baseline survey years, follow-up periods, and study populations. [32]
  • The head and neck cancer meta-analysis reports substantial heterogeneity across studies and notes possible differences in study design, quality, participant characteristics, and tobacco-smoking circumstances. [84]
  • The colorectal cancer meta-analysis reports considerable heterogeneity for the tobacco-smoking estimate. [70]
  • The Iranian cancer-patient review reports high heterogeneity in the pooled prevalence of tobacco use across studies. [33]
  • The breast cancer meta-analysis says evidence was limited and inconsistent in earlier IARC publications, and it also notes that some genetic subgroup findings were limited and not conclusive. [86]
  • The arsenic-smoking review says further exploration is necessary to understand the type of interaction between arsenic and tobacco smoking for risk assessment and health surveillance. [41]
  • The colorectal meta-analysis states that the association between smoking and early-onset colorectal neoplasms remains unclear in prior meta-analyses and that further studies are needed. [6]
  • The gastric cancer review says further investigations are needed to determine the value of post-operative gastric cancer surveillance after bariatric bypass surgery. [5]
  • The sources note that evidence is still limited for some smoking-cessation medications and e-health approaches in waterpipe users. [73]
  • The relapse review notes that many studies used nonstandardized relapse definitions and different follow-up time points, which limits interpretation. [90]
  • The Mendelian randomization review reports that some associations were not strong or coherent for several non-cancer outcomes, showing that not all smoking-disease links were equally supported across outcomes. [39]
  • The bladder cancer meta-analysis says further studies should report more detailed results by gender, age, region, and other risk factors to address residual confounding. [43]
  • The lung cancer systematic review says additional validation is required for the precise effect of smoking cessation after initial primary lung cancer diagnosis. [74]
  • The radon and tobacco smoke review notes that the interaction between radon exposure and smoking habit has not yet been quantitatively estimated in a fully settled way across all included studies. [94]
  • The thyroid-cancer meta-analysis says the evidence is equivocal and that additional large, well-designed epidemiological and experimental studies are needed. [47][28]
  • The smoking-reduction meta-analysis says the relationships between smoking reduction and several endpoints, including all-cause mortality and cardiovascular disease, remain unclear. [75]
  • The primary-melanoma-of-the-lung review says it is not clear whether cigarette smoking has a role in the onset of that rare cancer. [87]
  • The e-cigarette review says the evidence for a link with head and neck cancers is variable and that more longitudinal and controlled studies are needed. [77]
  • The ovarian cancer meta-analysis reports a non-significant linear relation for overall ovarian cancer and several histotypes with smoking intensity, duration, and time since quitting. [88]
  • The provided sources do not give a single pooled estimate for all cancer types combined for tobacco smoke exposure. [21][22][23]
  • The coffee meta-analysis says larger non-smoker populations are needed to confirm whether coffee drinking is associated with lung cancer after smoking is controlled for. [80]
  • The non-small cell lung cancer methylation meta-analysis notes that studies in other ethnic populations are needed and that gender and age could confound the findings. [53]
  • The urothelial carcinoma review says the evidence base lacks studies on smoking prognosis in numerous clinical demographic subgroups and lacks prospective investigation of smoking cessation. [30]
  • The intestinal metaplasia meta-analysis notes substantial heterogeneity across studies. [31]
  • The breast-cancer meta-analysis states that the relationship between active cigarette smoking and breast cancer risk remained controversial because of unresolved issues of confounding and dose response. [56]
  • The bladder-cancer meta-analysis reported substantial heterogeneity across studies, with I2 = 84.0% for the overall analysis. [57]
  • The NHL meta-analysis noted that future studies should assess smoking after diagnosis and whether pre-diagnosis smoking affects tumor molecular characteristics related to prognosis. [81]
  • The colorectal cancer literature described in the sources was previously inconsistent, and one meta-analysis noted that the association had been controversial. [65][66][62]
  • For liver cancer, one source notes that the IARC Monograph concluded the evidence for cigarette smoking was sufficient, while the US Surgeon General's report described the data as suggestive but not sufficient. [63]

Sources

Every statement above is drawn from these reviewed sources. This page reports what they describe. Sources last checked June 9, 2026.

  1. GuidelineVulvar Cancer, Version 3.2024, NCCN Clinical Practice Guidelines in Oncology · 2024
  2. GuidelineSmall cell lung cancer · 2013
  3. Systematic reviewSmoking and oral and pharyngeal cancer: a meta-analysis · 2026
  4. Systematic reviewEvaluation of dose-response relationships between smoking tobacco, alcohol consumption and oral cancer: a systematic review and meta-analysis · 2026
  5. Systematic reviewGastric cancer after Bariatric Bypass Surgery. Do they relate? (A Systematic Review) · 2023
  6. Meta-analysisSmoking as a risk factor for colorectal neoplasms in young individuals? A systematic meta-analysis · 2023
  7. Meta-analysisA comprehensive analysis of mRNA expression profiles of Esophageal Squamous Cell Carcinoma reveals downregulation of Desmoglein 1 and crucial genomic targets · 2023
  8. Meta-analysisAssociation of cigarette smoking habits with the risk of prostate cancer: a systematic review and meta-analysis · 2023
  9. Systematic reviewIs maternal smoking during pregnancy associated with childhood brain tumors? A systematic literature review · 2026
  10. Meta-analysisWine Consumption and Lung Cancer Risk: A Systematic Review and Meta-Analysis · 2025
  11. Meta-analysisAssociation between cigarette smoking and nasopharyngeal cancer risk: a meta-analysis · 2025
  12. Systematic reviewSmoking and bladder cancer: insights into pathogenesis and public health implications from a bibliometric analysis (1999-2023) · 2025
  13. Meta-analysisGastroesophageal disease risk and inhalational exposure a systematic review and meta-analysis · 2025
  14. Systematic reviewElectronic Cigarettes Versus Combustible Cigarettes in Oral Squamous Cell Cancer Patients: A Systematic Review · 2025
  15. Meta-analysisThe waterpipe smoking and human health: a systematic review and meta-analysis of 191 observational studies · 2025
  16. Meta-analysisRisk Factors for the Development of Barrett's Esophagus and Esophageal Adenocarcinoma: A Systematic Review and Meta-Analysis · 2025
  17. Systematic reviewComparative disease risks associated with cigarette smoking and use of moist smokeless tobacco and snus: an umbrella review of epidemiological evidence from the United States and Western Europe · 2025
  18. Meta-analysisSystematic review and meta-analysis corrected for history of smoking tobacco identifies type 1 diabetes as a possible risk factor for bladder cancer · 2025
  19. Meta-analysisEnvironmental Risk Factors for Gallbladder Cancer: Field-Wide Systematic Review and Meta-Analysis · 2025
  20. Meta-analysisParity and bladder cancer risk: a dose-response meta-analysis · 2017
  21. Meta-analysisLifestyle Risk Factors for Serrated Colorectal Polyps: A Systematic Review and Meta-analysis · 2017
  22. Meta-analysisSmoking Cessation and Risk of Esophageal Cancer by Histological Type: Systematic Review and Meta-analysis · 2017
  23. Meta-analysisLinking the generation of DNA adducts to lung cancer · 2017
  24. Meta-analysisCigarette smoking and the risk of nasopharyngeal carcinoma: a meta-analysis of epidemiological studies · 2017
  25. Meta-analysisRisk factors for neuroendocrine neoplasms: a systematic review and meta-analysis · 2016
  26. Systematic reviewTobacco smoking and methylation of genes related to lung cancer development · 2016
  27. Meta-analysisLifetime cigarette smoking and breast cancer prognosis in the After Breast Cancer Pooling Project · 2014
  28. Meta-analysisThyroid cancer risk and smoking status: a meta-analysis · 2014
  29. Meta-analysisGender susceptibility for cigarette smoking-attributable lung cancer: a systematic review and meta-analysis · 2014
  30. Systematic reviewEffect of smoking on outcomes of urothelial carcinoma: a systematic review of the literature · 2014
  31. Meta-analysisTobacco smoking and intestinal metaplasia: Systematic review and meta-analysis · 2014
  32. Meta-analysisSmoking-attributable Mortality in Korea, 2020: A Meta-analysis of 4 Databases · 2024
  33. Meta-analysisPrevalence of tobacco use among cancer patients in Iran: a systematic review and meta-analysis · 2024
  34. Meta-analysisEffect of smoking on melanoma incidence: a systematic review with meta-analysis · 2024
  35. Meta-analysisDose-risk relationships between cigarette smoking and cervical cancer: a systematic review and meta-analysis · 2023
  36. Meta-analysisEnvironmental and life-style risk factors for esophageal squamous cell carcinoma in Africa: a systematic review and meta-analysis · 2023
  37. Systematic reviewTobacco smoking influences the side effects of radiation therapy-managed patients with various malignancies: A systematic review · 2024
  38. Meta-analysisCancer-prone Phenotypes and Gene Expression Heterogeneity at Single-cell Resolution in Cigarette-smoking Lungs · 2023
  39. Meta-analysisAppraising the causal role of smoking in multiple diseases: A systematic review and meta-analysis of Mendelian randomization studies · 2022
  40. Systematic reviewEffectiveness of smoking cessation on the high-risk population of lung cancer with early screening: a systematic review and meta-analysis of randomized controlled trials until January 2022 · 2023
  41. Systematic reviewInteraction between Occupational and Non-Occupational Arsenic Exposure and Tobacco Smoke on Lung Cancerogenesis: A Systematic Review · 2023
  42. Meta-analysisCigarette smoking and risk of second primary cancer: a systematic review and meta-analysis · 2022
  43. Meta-analysisCigarette smoking and risk of bladder cancer: a dose-response meta-analysis · 2022
  44. Meta-analysisSecondhand smoke exposure and oral cancer risk: a systematic review and meta-analysis · 2022
  45. Systematic reviewRisk prediction models for esophageal cancer: A systematic review and critical appraisal · 2021
  46. Systematic reviewThe potential role of bacteria in pancreatic cancer: a systematic review · 2020
  47. Meta-analysisEffect of Cigarette Smoking on Thyroid Cancer: Meta-Analysis · 2021
  48. Systematic reviewStatistical projection methods for lung cancer incidence and mortality: a systematic review · 2019
  49. Meta-analysisLung cancer incidence in patients with schizophrenia: meta-analysis · 2019
  50. Systematic reviewRacial Disparities and Preventive Measures to Renal Cell Carcinoma · 2018
  51. Meta-analysisTobacco smoking and gastric cancer: meta-analyses of published data versus pooled analyses of individual participant data (StoP Project) · 2018
  52. Systematic reviewEpidemiology of Bladder Cancer: A Systematic Review and Contemporary Update of Risk Factors in 2018 · 2018
  53. Meta-analysisMeta-analyses of gene methylation and smoking behavior in non-small cell lung cancer patients · 2015
  54. Meta-analysisFruits, vegetables and lung cancer risk: a systematic review and meta-analysis · 2016
  55. Systematic reviewOral Cancer and Oral Precancerous Lesions in Inflammatory Bowel Diseases: A Systematic Review · 2015
  56. Meta-analysisActive smoking and breast cancer risk: original cohort data and meta-analysis · 2013
  57. Meta-analysisDiabetes mellitus and risk of bladder cancer: a meta-analysis of cohort studies · 2013
  58. Meta-analysisProfessional drivers and lung cancer: a systematic review and meta-analysis · 2012
  59. Meta-analysisTobacco smoking and esophageal and gastric cardia adenocarcinoma: a meta-analysis · 2011
  60. Meta-analysisThe effects of waterpipe tobacco smoking on health outcomes: a systematic review · 2010
  61. Meta-analysisTobacco smoking and cancer: a meta-analysis · 2008
  62. Meta-analysisSmoking and colorectal cancer: a meta-analysis · 2008
  63. Meta-analysisMeta-analysis of epidemiologic studies on cigarette smoking and liver cancer · 2009
  64. Meta-analysisSmoking and gastric cancer: systematic review and meta-analysis of cohort studies · 2008
  65. Meta-analysisCigarette smoking and colorectal cancer incidence and mortality: systematic review and meta-analysis · 2009
  66. Meta-analysisCigarette smoking and the risk of colorectal cancer: a meta-analysis of prospective cohort studies · 2009
  67. Meta-analysisEvaluating eight smoking metrics for modelling survival in non-small cell lung cancer · 2026
  68. Meta-analysisOral nicotine pouches for cessation or reduction of use of other tobacco or nicotine products · 2025
  69. Meta-analysisDose-response association between cigarette smoking and gastric cancer risk: a systematic review and meta-analysis · 2024
  70. Meta-analysisIncidence and risk factors for colorectal cancer in Africa: a systematic review and meta-analysis · 2024
  71. Meta-analysisPrevalence of cigarette and waterpipe smoking and associated cancer incidence among adults in the Middle East · 2023
  72. Systematic reviewPatterns of use, perceptions, and cardiopulmonary health risks of cigar products: a systematic review · 2023
  73. Meta-analysisInterventions for waterpipe smoking cessation · 2023
  74. Meta-analysisTobacco Smoking and Risk of Second Primary Lung Cancer · 2021
  75. Meta-analysisCigarette Smoking Reduction and Health Risks: A Systematic Review and Meta-analysis · 2021
  76. Meta-analysisDose-response relationships between cigarette smoking and kidney cancer: A systematic review and meta-analysis · 2019
  77. Systematic reviewE-cigarettes and head and neck cancers: A systematic review of the current literature · 2019
  78. Meta-analysisActive and passive smoking and risk of breast cancer: a meta-analysis · 2015
  79. Systematic reviewSystematic review of cigar smoking and all cause and smoking related mortality · 2015
  80. Meta-analysisCoffee Drinking and Risk of Lung Cancer-A Meta-Analysis · 2016
  81. Meta-analysisPre-diagnosis cigarette smoking and overall survival in non-Hodgkin lymphoma · 2013
  82. Systematic reviewThe risk of lung cancer from vaping or e-cigarette usage: a systematic review · 2025
  83. Systematic reviewIndirect adjustment of tobacco smoking in occupational studies of lung cancer: A systematic review of the available methods and their applications · 2025
  84. Meta-analysisReduction of head and neck cancer risk following smoking cessation: a systematic review and meta-analysis · 2024
  85. Systematic reviewEpidemiology of Bladder Cancer in 2023: A Systematic Review of Risk Factors · 2023
  86. Meta-analysisDose-response Relationships Between Cigarette Smoking and Breast Cancer Risk: A Systematic Review and Meta-analysis · 2023
  87. Systematic reviewPrimary Melanoma of the Lung: A Systematic Review · 2020
  88. Meta-analysisDose-risk relationships between cigarette smoking and ovarian cancer histotypes: a comprehensive meta-analysis · 2019
  89. GuidelineGerman-Austrian guideline on screening for anal dysplasia and anal carcinoma in people living with HIV · 2025
  90. Systematic reviewSystematic review of smoking relapse rates among cancer survivors who quit at the time of cancer diagnosis · 2022
  91. Systematic reviewPost-Breast Cancer Radiotherapy Bronchiolitis Obliterans Organizing Pneumonia · 2020
  92. Systematic reviewA systematic review of the factors associated with lung cancer stigma · 2026
  93. Systematic reviewThe impact of smoking on adjuvant breast cancer radiation treatment: A systematic review · 2020
  94. Systematic reviewInteraction between occupational radon exposure and tobacco smoke: a systematic review · 2022

Keep exploring

See the live research feed, the per-compound profiles in cancer-fighting agents, and the cancer-type guides. Everything across the site is built from the same reviewed, cited evidence.