Angioendotheliomatosis proliferans systemisata: an angiotropic neoplasm of lymphoid origin.

Angioendotheliomatosis proliferans systemisata (APS) is a rare disease entity characterized by intravascular proliferation of undifferentiated tumor cells and associated with complex vascular infolding, proliferation, and tortuosity. Most of the symptomatology results from the microinfarcts caused by clogging of the vessels. The most commonly affected sites are skin and central nervous system. In contrast to the earlier belief, there are distinct histopathologic differences between the so-called benign and malignant type, so that benign form should actually be excluded from the entity of APS. The majority of reported cases now appear to be of lymphoid cell origin, while few cases of other cancers have been reported to present as APS. The original concept of an endothelial origin of APS is in doubt, though a few cases of APS might prove to be endothelial in origin.