Distribution analyses of acquired melanocytic naevi on the trunk.

Acquired melanocytic naevi (AMN) are a well-known risk factor for the development of melanoma. Whereas previous studies have reviewed AMN distributions on individual body sites, the clinical distribution of AMN on the adult trunk has not been thoroughly investigated. We studied 40 participants with 1,282 naevi >5 mm, of which 781 were located on the trunk. Remarkably, 70% of these truncal naevi were located on the back and we produced a continuous mathematical description of decreasing naevus frequency moving dorsolaterally from the back midline. Furthermore we found that for both sexes the mean naevus size was larger on the front as well as on the lower trunk. This distinct pattern, whilst probably being unwritten knowledge (in the dermatology domain), has not been discussed before.