Angiotropic malignant melanoma. Report of two cases.

Two cases of malignant melanoma are described that showed focal perineural invasion and exhibited striking tropism for small and medium-sized vessels, primarily veins. The melanoma cells proliferated within the vessel walls, expanding and replacing the muscle layer but sparing the endothelia. Intravascular invasion was not seen. Immunohistochemical studies confirmed the pattern of growth within vessel walls and the integrity of their endothelia. In one of the cases, similar vascular tropism was encountered in a capsular vein from a regional lymph node. We propose the term "angiotropic malignant melanoma" for this phenomenon and suggest that angiotropism may be a rare mechanism for melanoma spread and progression.