Objective: To assess the risk of developing a basal cell carcinoma (BCC), and/or a squamous cell carcinoma (SCC), and/or Bowen disease (SCC in situ) after a nonmelanoma skin cancer (NMSC) of a specific type.
Data sources: Four electronic databases were searched from January 1, 1966, to October 21, 1999.
Study selection: We included all studies published in English, identified by standard search strategies, that provided original data quantifying the risk of an NMSC among persons with a previous NMSC.
Data extraction: For each study and separate histological type of index skin tumor and subsequent skin tumor (SCC, BCC, NMSC, or Bowen disease), we determined the 3-year cumulative risk and the incidence rate of second tumors per 100 000 person-years. In cases where more than 1 study was assessing the risk of one specific tumor type after another, we undertook a formal meta-analysis. We compared the incidence of a subsequent SCC after an index SCC and of a subsequent BCC after an index BCC with the incidence of the first occurrence of such tumors in the comparable general population.
Data synthesis: We identified and reviewed 17 studies that included data for 26 tumor combinations. Overall, the 3-year cumulative risk of a subsequent SCC after an index SCC is 18%, at least a 10-fold increase in incidence compared with the incidence of first tumors in a comparable general population. For BCCs, the 3-year cumulative risk is 44%, also at least a 10-fold increase in incidence compared with the rate in a comparable general population. The risk of developing a BCC in patients with a prior SCC is about equal to that risk among persons with a prior BCC, but the risk of developing an SCC in patients with a prior BCC is low (6%).
Conclusions: Although these studies vary in their study type, location, and biases, their results are consistent. The risk of developing a subsequent skin cancer of a specific type depends on the type of prior NMSC and number of prior skin tumors of that type. Based on these findings, follow-up strategies for patients with BCC and SCC are suggested.