Abstract

Pleomorphic hyalinizing angiectatic tumor (PHAT) is a rare, recently recognized neoplasm occurring predominantly in the subcutaneous tissue of the lower limbs of adults. We report a case of PHAT in an 83-year-old woman who presented with a 5.0 x 5.0 x 2.0 cm mass in the soft part of her left thigh. Histologically, the tumor was well circumscribed by a thin fibrous capsule and predominantly composed of fusiform cells with eosinophilic cytoplasm and round-to-oval or pleomorphic nuclei. The tumor cells resembled those of malignant fibrous histiocytoma, but differed from them by less prominent mitotic figures. Immunohistochemically, the tumor cells were diffusely and strongly positive for CD34; partially positive for vimentin and CD99 (MIC-2); and negative for epithelial and non-epithelial markers. Ultrastructurally, the tumor cells had pleomorphic cytoplasm and nucleus. Intermediate-sized cytoplasmic filaments were observed in a few tumor cells, but neurosecretory-type granule-like intracytoplasmic organelles were not seen. These findings suggest that this tumor is derived from stromal fibroblast, such as solitary fibrous tumors or giant cell angiofibroma.