Reporting regression with melanoma in situ: reappraisal of a potential paradox.

Melanoma in situ (MIS) is a form of radial growth phase melanoma in which the proliferation of malignant cells is confined to the epidermis. Histologic features are invaluable in recognition of MIS. Regression occurs when the host's immune system attacks the primary melanocytic tumor cells via tumor infiltrate lymphocytes, resulting in a fibrotic component. Various criteria have been proposed to assess the extent of histologic regression. Some authors define regression based on histologic features of the dermis, which is inappropriate for MIS. Specific dermatoscopic findings of regression in MIS have been reported including peppering, grey-blue areas, white areas, and blue-whitish veils. Many studies assess the impact of histologic regression on invasive melanoma prognosis, but no studies to-date have considered the effect of histologic regression exclusively in patients with MIS. The literature to-date does not suggest evaluation and management should be modified if histologic regression is present in MIS. Studies specifically investigating the effect of histologic regression on MIS prognosis are needed to inform evidence-based practices.