Incidence of keratinocyte carcinomas in Italy: an exercise in indirect estimation based on melanoma data

Background The occurrence of keratinocyte carcinomas (KC) worldwide appears to be increasing, however, information on the actual incidence of these tumours is often incomplete. Objectives The aim of this study was to provide information on the KC/melanoma ratio in order to indirectly estimate the occurrence of KC. Materials & Methods Data were collected according to a snowball sampling procedure between Italian dermatologists. Colleagues working on melanoma and non-melanoma units were excluded. These ratios were applied to estimates derived from histopathological records, namely melanoma incidence estimates available from the Italian National Cancer Registry Network. The final estimates for KC incidence were thus obtained using the formula: KC incidence (per 100,000) = melanoma incidence (per 100,000) * (KC/melanoma ratio). Results Our results revealed a BCC/melanoma ratio of 4.4 and SCC/melanoma ratio of 1.7; values that are approximately 4 to 5 times smaller than those self-reported by dermatologists. Interestingly, this large discrepancy was not observed for the BCC/SCC ratio, which was 2.5 in the north, 2.7 in the centre, and 3.2 in the south of Italy, with an overall value of 2.8. Based on the histopathological data, this ratio was 2.6. Conclusion In Italy, the actual occurrence of BCC and SCC seems to be vastly underestimated based on histopathological data, compared to data reported by dermatologists.