Glomangiosarcoma in a glomus tumor. An immunohistochemical and ultrastructural study.

An extremely rare case of glomangiosarcoma (GS) occurring in a glomus tumor (GT) was evaluated ultrastructurally and histochemically. A man 65 years of age who was suffering from back pain underwent resection of a deep cutaneous nodule. Cells of a solid type GT showed numerous subplasmalemmal pinocytotic vesicles, thin filaments with scattered dense bodies, and thick external lamina, but negative desmin staining and a lack of glycogen. Similar findings also were observed in the GS, but were less obvious. The GS compressed the surrounding GT, exhibited many mitotic figures, prominent nucleoli, elongated nuclei and cytoplasm, and reacted more strongly to vimentin staining than the GT. The GT contained S-100 protein-positive Schwann cells, a few substance P-positive nerve fibers, and moderate numbers of infiltrating mast cells. None of these findings were observed in the GS. Results were consistent with the view that GS was transformed possibly from the GT, and that the good prognosis for GS may be due to its small size that may be related to the preexistence of a pain-causing GT.