Normal Number of Melanocytes Defined

JACKSONVILLE, Florida—A Mayo Clinic physician and his colleagues have defined the normal number of melanocytes that are present in Caucasians' sun-exposed skin. Until now, there has not been a criterion to distinguish sun damage from early (in situ) melanoma. Lead author Ali Hendi, MD, and his team thought that pathologists and Mohs surgeons may err on the side of overdiagnosing melanoma in sun-damaged skin, leading to additional and unnecessary surgery, complications, or deformity. In the study, disease-free tissue samples were obtained from 149 randomly selected Caucasian patients undergoing Mohs surgery for nonmelanoma skin cancers of the face and neck (Arch Dermatol 142:871-876, 2006). They found that in normal sun-exposed skin, the mean number of melanocytes in a 0.5 mm diameter was 15.6 (range, 6 to 29). Adjacent melanocytes, another indicator used by pathologists to diagnose early melanoma, were present in varying degrees in all but 11% of the samples. Finally, melanocytes were found to descend along the hair follicles, a finding previously attributed only to melanoma in sun-damaged skin. Dr. Hendi said the findings are significant because many surgeons remove tissue until they reach undamaged cells with "normal" melanocyte distribution.