High incidence of second basal cell skin cancers.

We considered the risk of second basal cell cancers (BCC) of the skin using a population-based series of 1,868 BCC collected between 1976 and 1985 in the Swiss Cantons of Vaud and Neuchâtel, and followed-up to the end of 2003. Overall, 507 second BCC were observed versus 59.98 expected, corresponding to a standardized incidence ratio (SIR) of 8.45 (95% CI: 7.73-9.22). The SIRs were similar in men and women in subsequent calendar periods, but tended to decline with advancing age at diagnosis of first BCC, from 13.98 below age 50 to 7.13 at age 70 or over. Consequently, the rate of first BCC increased to approximately 30-fold between 7/100,000 at age 30-39 and 200/100,000 at age 70-79, but the rate of second BCC increased only about 3-fold between 31/1,000 at age 30-39 and 110/1,000 at age 70-79. The cumulative risk of second BCC was 11% at 5 years, 21% at 10 years and 40% at 20 years. This study indicates that the relative (but not the absolute) risk of second BCC is greater at younger age and declines with advancing age, and is therefore compatible with an excess baseline risk in a population of susceptible individuals.