Time trends and latitudinal differences in melanoma thickness distribution in Australia, 1990-2006

This study investigated time trends and latitude differentials in the thickness distributions of invasive melanomas diagnosed in Australia between 1990 and 2006 using data from population-based cancer registries. Trends in incidence rates were calculated by sex, age group, thickness, year at diagnosis and latitude. For thin (<1.00 mm) melanomas the increase was very pronounced during the early 1990s (1990-1996, annual percentage change and 95% confidence interval: males +5.6(+3.5,+7.7); females +4.1(+1.7,+6.5), but then incidence rates became stable among both males (+0.6(-0.1,+1.4)) and females (-0.0(-0.9,+0.9)) of all ages between 1996 and 2006. In contrast, incidence of thick (>4.00 mm) melanomas continued to increase over the entire period (males +2.6(+1.9,+3.4); females +1.6(+0.6,+2.6)). Recent reductions in the incidence of thin melanomas were observed among young (<50 years) males and females, contrasted by an increase in thin melanomas among older people, and increases in thick melanomas among most age groups for males and elderly (75+) females. A strong latitude gradient in incidence rates was observed, with rates being highest in northern, more tropical areas and lowest in the most southern regions. However, the magnitude of the increase in thick melanomas was most pronounced in southern parts of Australia. The observed trends in thin melanomas can most likely be attributed to the impact of early detection and skin awareness campaigns. However, these efforts have not impacted on the continued increase in the incidence of thick melanomas, although some increase may be due to earlier detection of metastasising melanomas. This highlights the need for continued vigilance in early detection processes.