Second primary malignancies in patients with non-melanoma skin cancer: Results from a cancer registry–based study in Emilia Romagna, north-east Italy

Background: previous research on the risk of subsequent, primary non-cutaneous malignancies among patients with non-melanoma skin cancers (NMSCs) led to conflicting results. We aimed to investigate a possible link between NMSC and second primary malignancies by using the population-based data available in cancer registries. Methods: this observational study retrospectively assessed the risk of occurrence of both synchronous and methachronous second primary tumours in a cohort of cancer patients whose first diagnosis was NMSC. The cohort came from the network of general cancer registries of the Emilia-Romagna Region, northeast Italy, in the period between 1978 and 2012, and was compared with the general population living in the same area. Two main indexes were used: i) Standardized Incidence Ratio (SIR), calculated as the ratio between the observed and the expected number of second cancers and ii) Excess Absolute Risk (EAR), expressing the absolute excess or deficit of second cancer incidence. Results: in the period analysed (1978–2012, 72,503,157 person/years, PYs), 89,912 primary NMSC were found in 76,414 patients. Among them, 14,195 developed a second primary cancer in the subsequent 501,763 follow-up PYs. NMSC patients showed an overall SIR of 1.22 (CI 95% 1.20-1,24) and an EAR of 5.11 cases/1000 PYs (CI 95% 4.48–5.74). Conclusions: the study results showed that NMSC patients had an increase in relative risk and, at least for some tumours, in absolute risk of developing a second cancer when compared with the general population. Genetic, environmental and personal risk factors may influence this finding.