HISTOLOGIC REGRESSION IN MALIGNANT-MELANOMA - AN INTEROBSERVER CONCORDANCE STUDY

Histologic evidence for regression as a prognostic indicator in melano ma has shown conflicting results. To assess if melanoma regression is a consistently identifiable histologic feature, an interobserver conco rdance study was undertaken. Fifty histologic slides of melanoma with Breslow thickness of 1 mm or less were non-randomly selected from the Massachusetts General Hospital Melanoma Registry. The selection was in favor of those with regression present in 44 of 50 slides (88%). Two dermatopathologists working independently evaluated a 2 mm wide bracke ted area in each tissue section and then the remainder of the non-brac keted tissue section for regression. Before and after each slide revie w, the evaluators were required to read criteria for early, intermedia te, and late regression explicitly outlined. The overall concordance r ate for the presence and absence of regression was 96% (48/50) in the bracketed area and 90% for the outside area. When the group with regre ssion was subdivided into three stages, interobserver agreement fell t o 86% for the bracketed, and 66% for the outside area. In at least 30% of cases where regression was detected in the bracketed area, both re viewers observed two or more stages of regression in the remainder of tissue section. Therefore, subdividing the process is impractical and unrealistic. Consistent histologic identification of regression in mel anoma requires a simple and systematic approach which should be applie d to future studies that include melanoma regression as a prognostic f actor.