[Basal cell carcinoma: often more than one].
OBJECTIVE To calculate the cumulative risks and incidence rates for the development of multiple (two or more) basal cell carcinomas (BCC). DESIGN A retrospective cohort study with data from PALGA, the nationwide network and registry of histopathology and cytopathology in the Netherlands. METHOD Using pathology reports, the first 2483 patients diagnosed with a first histologically confirmed BCC in the year 2004 were retrospectively followed for 5 years. The Andersen-Gill survival analysis was used to study whether gender or age affected the risk of developing multiple BCCs. RESULTS In total, 2483 patients developed 3793 BCCs. The five-year cumulative risk of developing multiple BCCs was 29.2%. The incidence rate for the development of two or more BCCs was 25,318 per 100,000 person-years in the first half year after first BCC diagnosis, decreasing to 6953 per 100,000 person-years after 5 years of follow-up. Compared with women men had a 30% (adjusted HR 1.30; 95% CI 1.11-1.53) higher risk of developing multiple BCCs and those aged 65-79 years had an 80% (adjusted HR 1.81; 95% CI 1.37-2.41) higher risk of having two or more BCCs compared with patients younger than 50 years. CONCLUSION Almost one third of the patients with a BCC developed two or more BCCs, most frequently in the period shortly after the first BCC. At diagnosis of BCC a full body skin examination should be performed and repeated annually for at least three years.