Abstract

Solitary fibrous tumor (SFT) accounts for approximately 2% of all soft tissue tumors. While SFTs most frequently occur in deep soft tissue, the pleura, and the abdominal cavity, retroperitoneum, and pelvis, they can arise in almost any anatomical location, superficial or deep. We present a case of a 74-year-old man with history of basal cell carcinoma of the ear who presents to the clinic with a newly recognized pedunculated pink papule on his left heel. Microscopic examination reveals a dermally centered, nodular, well-circumscribed, cellular spindle cell mesenchymal neoplasm composed of fusiform to ovoid cells that are arranged haphazardly and in short, ill-defined fascicles in a variably myxocollagenous to densely collagenized matrix. Additionally, the tumor shows scattered cells with enlarged and/or multiple nuclei, staghorn-like vessels, and entrapment of adnexal structures with surrounding sclerosis. No tumor necrosis is identified, but mitoses focally number 4 per 10 high-power-fields. The differential diagnosis for cutaneous solitary fibrous tumor includes other dermal soft tissue neoplasms, such as dermatofibrosarcoma protuberans, and perivascular myoid neoplasms, such as myopericytoma/myofibroma, but the immunohistochemical staining profile of these tumors differs from that of SFT. The presence of diffuse immunoreactivity for STAT6 supports the diagnosis of solitary fibrous tumor in this highly unusual acral cutaneous location.