Proliferation marker Ki-S5 as a diagnostic tool in melanocytic lesions.

Abstract

A discrimination between benign and malignant melanocytic lesions is not always possible by conventional histology. Our purpose was to determine the proliferative activity in various types of melanocytic neoplasms and to appraise its value as a diagnostic adjunct. The growth fraction was assessed immunohistochemically in 398 melanocytic lesions by means of the monoclonal antibody Ki-S5 directed to the Ki-67 antigen. In this way, a cut-off level was defined and applied to 112 lesions of equivocal histology. The revised diagnoses were correlated to the clinical courses. Common nevi, Spitz nevi, and melanomas exhibited significantly different proliferation indices and distinctive distribution patterns of cycling cells. In agreement, malignancy diagnosed on the basis of a growth fraction greater than 5% was confirmed by disease progression in 68% of our cases with uncertain diagnosis. Determination of the proliferative activity in melanocytic lesions may usefully complement conventional histology to improve diagnostic accuracy.