Smoking is consistently seen as a risk for various cancers, and in recent years it has been connected to colorectal cancer in particular. In 2014, the US Surgeon General issued a report on tobacco claiming smoking as a direct cause of colorectal and liver cancer, and a factor that increases the failure rate of cancer treatment.¹

Several studies have been conducted that assess the link between smoking and colorectal cancer, including one in 2020 in the American Journal of Epidemiology examining how anatomic subsite and sex affect risk.² What are some of the specific colorectal cancer risks clinicians can discuss with patients who smoke?

  1. Sex disparities

This study evaluated more than 215,000 men and women from 45 to 75 years old. These participants were enrolled from 1993 to 1996 and answered a questionnaire that included information on their smoking habits and ascertained information on colorectal cancer history through either their death or through December 31, 2013.

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The researchers found that while female smokers had less pack-years of smoking than male smokers, both sexes had similar smoking-related risk for colorectal cancer. Clinicians should make their female patients aware that they may be putting themselves at significant risk for colorectal cancer regardless of how long they have been smoking.

  1. Postmenopausal risk

The researchers also found that postmenopausal women in particular had high smoking-related risk of right colon cancer. This finding held true regardless of whether participants had undergone hormone therapy during menopause. When discussing smoking-related risks for women, physicians should let these patients know that they may face even greater risk once they go through menopause.

  1. Earlier onset of cancer

An October 2020 study published in Cancer Research and Management investigated colorectal cancer risk factors and found tobacco use to be a significant contributing factor.³ In addition to estimating that 12% of colorectal cancer deaths can be attributed to tobacco use, the researchers claim that smokers showed an earlier average age of onset of colorectal cancer.

  1. Association with alcohol consumption

Frequent alcohol consumption has also been associated with colorectal cancer risk. Patients who smoke should be advised of this, as there can be a social relationship between alcohol and tobacco use that can potentially increase add risk.

  1. Active smoking

Smoking in tandem with certain diseases may present individuals with unique risks. A 2020 study published in Medicine (Baltimore) looked at risk factors associated with colorectal cancer in patients with ulcerative colitis.⁴ The researchers found that while only 5.5% of the 254 subjects were smokers at their last recorded appointment, active smoking was a significant risk factor for colorectal cancer. In this study, former smokers were categorized as nonsmokers.

Although any smoking history may be a risk for colorectal cancer, medical professionals may want to warn patients that active and prolonged smoking habits may present an added risk for them.


  1. Health consequences of smoking, Surgeon General fact sheet. Health and Human Services. Reviewed January 16, 2014. Accessed December 9, 2020.
  2. Gram IT, Park S-Y, Wilkens LR, Haiman CA, Le Marchand L. Smoking-related risks of colorectal cancer by anatomical subsite and sex. Am J Epidemiol. 2020;189(6):543-553. doi:10.1093/aje/kwaa005
  3. Hull R, Francies FZ, Oyomno M, Dlamini Z. Colorectal cancer genetics, incidence and risk factors: in search for targeted therapies. Cancer Manag Res. 2020;12:9869-9882 doi:10.2147/CMAR.S251223
  4. de Campos Silva EF, Baima JP, de Barros JR, et al. Risk factors for ulcerative colitis-associated colorectal cancer: a retrospective cohort study.Medicine (Baltimore). 2020;99(32):e21686. doi:10.1097/md.0000000000021686