Associations between smoking status and stage of colorectal cancer at diagnosis in Massachusetts between 1982 and 1987.

To examine the relationship between smoking and stage of colorectal cancer at diagnosis, data on 2788 current smokers and 6313 nonsmokers with known stage at diagnosis were obtained from the Massachusetts Cancer Registry. The stage at diagnosis was treated as a polytomous response variable in a logit-type, log-linear (Poisson) model, with smoking status, age, sex, and race as covariates. The relative frequency of disseminated colorectal cancer was 45% greater in smokers, compared with nonsmokers (relative risk [RR] = 1.45; 95% confidence interval, 1.00 to 2.09). A substudy was conducted to determine the accuracy of the registry's smoking data; the findings suggest that the actual association may be larger than that presented above. These results confirm the presence of an association between smoking and advanced stage of colorectal cancer at diagnosis. Whether the association is due to a biologic or behavioral phenomenon cannot be determined from these data.