The many faces of completely regressed malignant melanoma.

The prognostic significance of clinical and histologic regression of malignant melanoma is highly controversial. Although small foci of regression in evolving malignant melanomas seem to have little or no effect on morbidity and mortality, extensive regression in larger, fully evolved lesions may be associated with poor prognosis. This chapter emphasizes the histologic features of regression and the patterns that are responsible for diagnostic pitfalls.