Timing of subsequent new tumors in patients who present with basal cell carcinoma or cutaneous squamous cell carcinoma.

IMPORTANCE Patients with basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (SCC) (often termed nonmelanoma skin cancer or keratinocyte carcinoma [KC]) often develop new KCs, but information is limited on the frequency and timing of these subsequent tumors. This information is crucial to guide follow-up care. OBJECTIVE To determine the timing of subsequent new KCs in patients who present with KC. DESIGN, SETTING, AND PARTICIPANTS We enrolled a consecutive cohort of 1426 patients diagnosed as having biopsy-proven KC from January 1, 1999, through December 31, 2000, in a university dermatology practice and its affiliated Department of Veterans Affairs dermatology service. After exclusion of patients with basal cell nevus syndrome and immunocompromise, 1284 patients (90.0%) were followed up prospectively for a mean of 5.7 (range, 0-12.3) years. MAIN OUTCOMES AND MEASURES We assessed the risks for subsequent KCs over time using single-failure and multiple-failure models. We separately assessed outcomes after first lifetime KCs and after nonfirst lifetime KCs. We also performed secondary analyses of the risk for a subsequent BCC after a prior BCC diagnosis and the risk for a subsequent SCC after a prior SCC diagnosis. RESULTS The risk for a subsequent KC was substantially lower after the first lifetime KC diagnosis: 14.5% (95% CI, 11.9%-17.7%) at 1 year, 31.1% (95% CI, 27.3%-35.3%) at 3 years, and 40.7% (95% CI, 36.5%-45.2%) at 5 years, than after a nonfirst KC: 43.9% (95% CI, 42.0%-45.9%) at 1 year, 71.1% (95% CI, 69.1%-73.0%) at 3 years, and 82.0% (95% CI, 80.2%-83.7%) at 5 years. Secondary analyses of the risks for a subsequent BCC after a prior BCC diagnosis and of a subsequent SCC after a prior SCC diagnosis yielded results consistent with the analyses for the pooled KC sample. CONCLUSIONS AND RELEVANCE Although all patients with KC are assumed to be at high risk for subsequent tumors, a subset may not develop another KC after their first tumor. Whether these findings are related to biological or behavioral differences or to differences in health care services should be investigated further to inform and improve care. Ongoing routine screening for subsequent KC may not be indicated for all patients with KC. Skin cancer screening can be improved with a better understanding of the course and frequency of subsequent KC diagnoses.