Incidence trends of melanoma of the skin compared with other localisations, in the Norwegian population, 1956-2005

Background: Increasing incidence rates (IRs) of cutaneous malignant melanoma (CMM) have been associated with increased exposure to ultraviolet radiation (UVR). The aim of this study was to compare the changes over time in IRs of malignant melanoma in anatomical localisations exposed to different levels of UVR in the same population. Patients and methods: All incident cases of melanoma (invasive) diagnosed 1956-2005 were extracted from the database of the Cancer Registry of Norway. The average percentage change of the age-standardised IRs per 5-year period of diagnosis was calculated (loglinear regression) by anatomical localisation (skin, eye, internal organs and external genitalia). Results: CMM represented 91.7% of the total number of melanomas, while ocular melanoma and melanoma in the internal organs represented 6.2% and 1.2%, respectively. The average quinquennal percentage increase in IRs for CMM and melanoma in internal organs was 23.3% [95% confidence interval (CI) 20.9-25.8] and 14.0% (95% CI 8.2-19.7), respectively. The corresponding analysis for ocular melanoma showed an increase of 1.3% (95% CI -1.5 to 4.2) and a decrease (not significant) for melanoma on male (-8.8%) and female (-2.1%) external genitalia. Conclusion: A wide variation in IRs and trends between the four anatomical localisations with unlike levels of UVR exposure suggests different causal pathways for melanoma.