Site-specific risk of cutaneous malignant melanoma and pattern of Sun exposure in New Zealand

The site-specific relationship between melanoma and sun exposure was investigated in the high-risk region of New Zealand. Age and latitude of residence were used as biological and geographical proxy measures of exposure for the 16,117 newly incident cases and 3,150 death records reported between 1968 and 1993. Age-standardized rates were the highest for the trunk in males and for the lower limbs in females, but once body surface area was accounted for, highest rates were found on fully exposed sites, particularly the ears in men. Melanomas occurred at a substantially younger age on intermittently exposed sites than chronically exposed ones (difference of about 13 and 27 years for men and women, respectively, between the trunk and the face). Age and latitude were found to influence melanoma rates in a sex- and site-specific fashion. For heavily exposed body areas, incidence rates increased more modestly with age before age 50 than after. In contrast, sharp increases in risk occurred from early age for episodically exposed sites with a reversal of trend observed among the elderly. For males, the magnitude of the latitude gradient was about 65% (incidence) and 50% (mortality) greater for body areas most intermittently exposed compared with those with a least intermittent pattern of exposure. The latitude gradient was steeper for males than females and for incidence than mortality, regardless of the pattern of site exposure. Sex- and age-specific differences in risk were largely explained by the varying patterns of exposure. These results confirm that intermittent exposure is probably more effective than continuous exposure in producing an early onset of melanoma. Reducing the episodes of acute exposure remains a paramount aspect to melanoma prevention strategies.