Completeness of data on malignant melanoma skin sites and morphology in the Croatian national cancer registry 2000-2014

Mortality rates and five-year relative survival for malignant melanoma (MM) of the skin in Croatia are poor compared with most European countries. Epidemiological data recorded at the National Cancer Registry (CNCR) are used for informing various decision-makers and researchers, as well as for comparisons with other countries. We analyzed CNCR data on MM skin and morphology for 2000-2007 and 2008-2014 and compared them with European 2000-2007 data. We further stratified skin site analyses in Croatia by sex, different age groups, and sources of reports. We found 52% of case with “non-specified sites” in Croatia in 2000-2007; however, that proportion decreased to 36% in 2008-2014, with 29% of registered MM cases occurring on the trunk, 22% on the limbs, and 13% on the head and neck. The proportion of “non-specified sites” cases in reports originating from university hospitals decreased by 25% and by 9.2% in those from general hospitals. The proportion of “not otherwise specified” among histologically verified cases decreased from 96% in 2000-2007 to 84% in 2008-2014. Our results reveal a substantial ratio of inadequately reported cases, in particular when compared to data at the European level, where in 2000-2007 only 7.7% of cases were from “non-specified sites” and 19% were of non-specified morphology. Irrespective of recent progress, the ratio of unspecified cases still hampers insight into site distribution by subgroups. A further increase in the overall completeness of MM data within CNCR is needed to enable research-informed improvement of melanoma control in the country. Our findings call for engagement of all stakeholders in optimization of the national melanoma registration processes and using models such as Regis-Tree