Prediagnostic smoking history, alcohol consumption, and colorectal cancer survival: the Seattle Colon Cancer Family Registry.

BACKGROUND: Smoking and alcohol consumption are associated with an increased risk of developing colorectal cancer. However, it is unclear whether these exposures are associated with survival after colorectal cancer diagnosis.
METHODS: Men and women diagnosed with incident colorectal cancer between 1998 and 2007 in 13 counties in western Washington State were identified by using the Surveillance, Epidemiology, and End Results cancer registry. Information on smoking history and alcohol consumption was collected by telephone interview. Follow-up for mortality was completed through linkage to the National Death Index. Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for associations among smoking, alcohol consumption, and mortality after colorectal cancer diagnosis. Stratified analyses were conducted by sex, age at diagnosis (<50 years, ≥ 50 years), tumor site (proximal, distal, rectal), stage (I-II, III-IV), and microsatellite instability status (stable/low, high).
RESULTS: Disease-specific and all-cause mortality were significantly higher for smokers (HR, 1.30; 95% CI, 1.09-1.74) compared with never-smokers (HR, 1.51; 95% CI, 1.24-1.83). However, this association was most prominent in those with tumors exhibiting high microsatellite instability (HR, 3.83; 95% CI, 1.32-11.11) and did not extend to those with rectal cancer (HR, 1.08; 95% CI, 0.72-1.61) or those diagnosed before age 50 years (HR, 0.99; 95% CI, 0.67-1.48). Alcohol consumption was not associated with disease-specific or all-cause mortality, regardless of patient or tumor characteristics.
CONCLUSIONS: In addition to an association with disease risk, smoking is associated with increased mortality after colorectal cancer diagnosis. This association is especially pronounced for colorectal cancer with high microsatellite instability.