International patterns suggest germ cell testicular cancer (GCTC) incidence may be lower in lower latitudes. To investigate this possibility, we examined GCTC incidence by latitude (population-centroid in 2000) for men >15 years within two reasonably homogeneous countries, the United States (US) and Australia. In the US, we examined age-adjusted incidence/latitude trends using data from states (2001-2010) and local-area registries (1980-2011). In Australia, we evaluated incidence/latitude trends in 61 Statistical Divisions (2000-2009). In White US men (68,566 cases), state incidences increased by latitude, rising 5.74% (4.45-7.05%) per 5°North latitude increment. Similar trends were found for seminoma and non-seminoma subtypes (p<0.001). In Black US men (2,256 cases), the association was also seen (4.9%; 0.2 to 9.7%). In local US data, similar increases in incidence with latitude were present in each of the last three decades. In Australia (6,042 cases), the incidence increased by 4.43% (95% CI: 1.54-7.39%) per 5°South, and trends for subtypes were similar. Thus, we found that incidence of GCTC in both White and Black men increased significantly with distance from the equator, approximately 1% per degree within the range of latitudes studied.
Photochemistry and Photobiology / Vol. 92, No. 5, pp.735-741