Incidence trends and familial risks in invasive and in situ cutaneous melanoma by sun-exposed body sites.

We studied incidence trends, age-incidence relationships and familial risks in invasive and in situ cutaneous melanoma, based on the Swedish Family-Cancer Database of more than 10 million individuals. Offspring were 0-66 years of age. Cancers were obtained from the Swedish Cancer Registry from years 1961-98. The study was based on 9,771 offspring and 22,888 parents with invasive melanoma and 2,446 offspring and 5,017 parents with in situ melanoma. Incidence rates increased markedly for invasive melanoma in the trunk. For in situ melanoma, trunk and head and neck were affected, and, in addition, legs for women. The maximal incidence was around age 80 years, independent of the type or site in men; in women early onset superficially spreading melanoma shifted the age for maximal incidence to about 60 years. For in situ melanoma, lentigo maligna was the main histogenetic type in the head and neck but in the trunk and legs superficially spreading melanoma was somewhat more common. Standardized incidence ratios (SIR) were calculated for familial risk at exposed and covered sites. The combined familial risks for invasive and in situ melanoma were higher at covered (SIR 3.56 from parents) than sun-exposed (1.92 from parents) sites and they agreed when familiality was defined between parents and offspring or between siblings; the sibling SIRs were 3.90 at covered and 2.53 at exposed sites. The data suggest that the higher melanoma density at exposed sites masks familial effects. Furthermore, sun exposure does not appear to reinforce the familial effect.