Smoking as a Primary Risk Factor
The relationships between tobacco use and cancers of the lung and head and neck have been established for almost 50 years. Of the estimated 53,000 cases of head and neck cancer diagnosed each year, 85% are associated with tobacco use. The relative attributable risk of morbidity from smoking for lung cancer is more than 90%; it is between 60% and 70% for other smoking-related cancers (larynx, oral cavity, esophagus, bladder, kidney, pancreas, and other urinary cancers). Evidence suggests that smoking before age 30 years is a strong risk factor for colorectal cancer, with the risk appearing after a very long induction period (>35 years) in both men  and women.
Smokers may also be at increased risk of regional and metastatic disease at diagnosis. In one study, smoking worsened the course or outcome of acute myeloid leukemia, particularly in younger patients and those with unfavorable karyotypes. A study of renal cell carcinoma patients suggests that improvement in renal cell carcinoma risk after smoking cessation may be relatively linear but may take more than 20 years to reduce risk to that of a nonsmoker.
Smoking contributes to cancer development by causing mutations in tumor suppressor genes and dominant oncogenes and by impairing mucociliary clearance in the lungs and decreasing immunologic response. (Refer to the PDQ summary on Lung Cancer Prevention for more information.)
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