Does relative melanoma distribution by body site 1960-2004 reflect changes in intermittent exposure and intentional tanning in the Swedish population?

Intermittent exposure to UV-radiation at an early age is a known important factor the aetiology of malignant melanoma. We surveyed data from the Swedish Cancer Registry for melanoma by body site for age and gender cohorts from 1960 to 2004, in an attempt to discern a reflection of major behavioural and societal changes in the relative distribution of melanoma by body site. The study comprised patients with malignant melanoma from the Swedish Cancer Registry, including information on body site of tumour (January 1, 1960 - December 31, 2004). In total, 46,337 malignant melanomas were diagnosed in 44,623 patients. Trends were assessed by incidence per site, and relative site distribution per age group and calendar period, and dividing body sites by exposure type to the sun: head (mostly continuous), trunk (mostly intermittent), and limbs (mixed exposure). Between calendar periods 1960-1964 and 2000-2004 melanomas increased most rapidly on the upper limbs (men 885%, women 1216%) on the trunk (men 729%, women 759%) and on the lower limbs (men 418%, women 289%) in both genders. The incidence increase of head tumors was slower. Across the life span, melanomas of the trunk and lower limbs dominate among patients < 70 years, whereas tumors of the head are most common among patients >= 70 years. Tumors of the trunk formed an increasing proportion of all melanomas during the period studied, particularly in females. The relative shift of melanomas from the head to the trunk with mostly intermittent UV exposure coincides with behavioral and societal changes with regard to sun exposure. This supports the hypothesis of a relationship between intentional exposure to ultraviolet radiation and malignant melanoma.