Background: Persons with basal cell skin cancer (BCSC) have shown increased risk of developing cancer at several other sites. Methods: We identified 3164 persons with BCSC and 15,730 comparison subjects matched for age, sex, race, residence area and length of membership in a health maintenance organization. Results: In retrospective follow-up for up to 24 years (mean 11.3 years), BCSC patients experienced statistically significant increases in the incidence of all cancer (relative risk [RR] = 1.2, 95% confidence interval [CI] = 1.1-1.4) lung cancer (RR = 1.4, CI = 1.0-1.8) and melanoma (RR = 2.2, CI = 1.6-3.0). Women experienced significantly increased risk for all cancer, lung cancer, melanoma and thyroid cancer, increases of borderline significance in breast cancer, non-Hodgkin's lymphoma and leukemia, and increased pre-existing bladder cancer. Men showed statistically significant increases in all cancer, melanoma, and kidney cancers, and mouth and throat cancers. Multivariate analysis incorporating available risk factor data did not weaken positive associations with BCSC except slightly for melanoma and for bladder cancer in women. Other previously reported associations were not confirmed. Conclusion: Periodic skin examinations appear well justified after removal of BCSC to detect new skin cancers including melanoma. Given the relatively weak, unexplained associations of BCSC with internal cancers, the costs vs. benefits of extra efforts to detect the latter still need to be determined.
