Time trends and latitude dependence of uveal and cutaneous malignant melanoma induced by solar radiation

Abstract

In order to evaluate the role of solar radiation in uveal melanoma etiology, the time and latitude dependency of the incidence rates of this melanoma type were studied in comparison with those of cutaneous malignant melanoma (CMM). Norway and several other countries with Caucasian populations were included. There is a marked north - south gradient of the incidence rates of CMM in Norway, with three times higher rates in the south than in the north. No such gradient is found for uveal melanoma. Similar findings have been published for CMM in other Caucasian populations, with the exception of Europe as a whole. In most populations the ratios of uveal melanoma incidence rates to those of CMM tend to decrease with increasing CMM rates. This is also true for Europe, in spite of the fact that in this region there is an inverse latitude gradient of CMM, with higher rates in the north than in the south.

In Norway the incidence rates of CMM have increased until about 1990 but have been constant, or even decreased (for young people) after that time, indicating constant or decreasing sun exposure. The uveal melanoma rates have been increasing after 1990. In most other populations the incidence rates of CMM have been increasing until recently while those of uveal melanoma have been decreasing. These data generally support the assumption that uveal melanomas are not generated by ultraviolet (UV) radiation and that solar UV, via its role in vitamin D photosynthesis, may have a protective effect.

Acknowledgements

The present work was supported by the Research Council of Norway (Norges forskningsråd) and the Norwegian Cancer Society (Kreftforeningen).

Figures and Tables

Figure 1 Time trends of the incidence rates (IR) of CMM and uveal melanoma in Norway for the period 1993–2004. For CMM over all data (men and women, age adjusted. Rates for persons below 50 years (all country) are shown separately).

Figure 2 The ratio of the number of uveal melanomas to that of CMM in Norway for three periods. Data shown separately for women and men.

Figure 3 The age adjusted incidence rates (IR) of CMM (per 10,000) and uveal melanoma (per 10,00,000) in Sweden, (A) for men, (B) for women. The ratio of the incidence rates of uveal melanoma to CMM is shown at the bottom of the panels in open triangles.

Figure 4 Age adjusted incidence rates (IR) of uveal melanomas as a function of the incidence rates of CMM (A men, B women) for some countries selected on the basis of our earlier CMM work.12

Figure 5 The ratio of the incidence rates (IR) of uveal melanoma to CMM as a function of the incidence rates of CMM for the same countries as those included in Figure 4.

Figure 6 Incidence rates (IR) of CMM per 1,00,000 (A), uveal melanoma per 10,00,000 (B) and the ratio (C) as functions of latitude. Melanoma data were extracted from the work of Virgili et al.38 Data refer to the period 1983–1994 and are from Ragusa (37°C), Tarragona (41°C), Navarra (43°C), Parma (45°C), Geneva (46°C), Slovenia (46°C), Bas Rhin (48°C), Saarland (49°C), CalvadosGen (49°C), Slovakia (49°C), Cracow (50°C), Eindhoven (51°C), West Midlands (53°C), Mersey (53°C), Yorkshire (54°C), Scotland (56°C), Denmark (56°C), Estonia (59°C), Sweden (62°C), Norway (62°C), Finland (64°C) and Iceland (65°C).

Figure 7 The annual percent changes of CMM and uveal melanomas death rates as taken from references.1,39 Average values for the time period from 1951 to 1978.