Colorectal cancer is the second leading cause of cancer deaths, according to background information in the article. Screening asymptomatic patients is an important strategy for reducing these deaths, because by the time patients experience symptoms, the cancer may have progressed beyond the point where it can be cured. Generally, physicians recommend that patients begin screening at age 50 years, the authors write. However, physicians might recommend that individuals with certain risk factors, including family history, begin screening at earlier ages. Screening methods include flexible sigmoidoscopy, which involves inserting a flexible optical instrument through the rectum into the lower portion of the large intestine, and colonoscopy, which involves inserting a longer flexible optical instrument through the rectum and into the entire colon, is more expensive, has higher complication rates and usually is performed by a gastroenterologist or surgeon rather than a primary care physician.

Anna L. Zisman, M.D., and colleagues at Evanston-Northwestern Healthcare, Feinberg School of Medicine, Northwestern University, Evanston, Ill., examined the records of 161,172 patients with colorectal cancer to assess whether certain risk factors, alcohol and tobacco use, should also be considered in screening decisions. They analyzed the relationship between use of these substances and age of onset of colon cancer as well as location of onset--distal or proximal colon. Distal tumors, including those in the lower left part of the colon and the rectum, can generally be detected by flexible sigmoidoscopy, while proximal tumors in the right side of the colon can be missed by methods other than colonoscopy.

Patients who were classified as alcohol or tobacco users, defined as those who had smoked or drank alcohol in the previous year, developed cancer at a younger age than non-drinkers and non-smokers. Current alcohol and tobacco users developed cancer an average of 7.8 years earlier (age 63.2 years in women and 62.1 years in men) than those who had never drank or smoked. Those who had never smoked but drank or who had never drank but smoked were each an average of 5.2 years younger at cancer diagnosis than those who neither smoked nor drank. Individuals who stopped drinking one year or more prior to the study and had never smoked developed cancer an average of 2.1 years earlier than those who had never drank or smoked. The effect of smoking appeared to be particularly large for women; women who smoke but never drank developed cancer 6.3 years younger than those who never drank or smoked, compared with 3.7 years in men. In additional, current alcohol and tobacco consumption was associated with an increased likelihood of distal colorectal cancer, although women in all categories were less likely to have distal cancer than men.

These findings suggest that individuals who smoke and drink should undergo screening for colorectal cancer beginning at a younger age, the authors write. In addition, women who do not smoke or drink may be more prone to proximal cancers and might therefore want to consider undergoing colonoscopy instead of flexible sigmoidoscopy. "In the future, we envision the development of risk scores with exogenous (e.g., alcohol and tobacco use, age, body mass index, diet and calcium consumption) and hereditary factors to tailor an individual's colorectal cancer screening program," they conclude.

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