Dying dogma: the pathological diagnosis of epidermotropic metastatic malignant melanoma.

Distinguishing primary cancer from a metastasis is a fundamental task in surgical pathology that has crucial therapeutic and prognostic implications. When metastatic melanoma involves the skin and extends into the epidermis (epidermotropic), differentiating it from primary cutaneous melanoma may be particularly difficult. Early investigators dismissed this issue as a nonproblem and dogmatically declared that junctional change was requisite for the diagnosis of primary cutaneous melanoma. Epidermotropic metastases of malignant melanoma (EMMM) are now recognized to have many features in common with primary melanoma, which can include involvement of the dermal-epidermal junction, extension of the intraepidermal component beyond the dermal component, and even an epidermal-only pattern. This article traces the evolution in criteria used to diagnose EMMM and highlights why much of the original thinking is no longer accepted. Current concepts in EMMM morphology are elaborated and illustrated. The role of immunomicroscopy and molecular pathology in the detection of EMMM is also discussed.