Dear Editor:Solitary fibrous tumor (SFT) is uncommon fibroblastic mesenchymal tumor that commonly affects pleura and peritoneum1. Despite multiple reports of SFT in various organs, cutaneous SFT is rare and few case reports have been issued. Furthermore, malignant cutaneous SFT is exceptional2. To our knowledge, this is only the second report of malignant SFT of the skin. We received the patient's consent form about publishing all photographic materials.59-year-old man presented with a protruding mass on his right shoulder, which had grown slowly over 10 years. The 5.0×4.3 cm-sized tumor was relatively hard and telangiectasia was observed on its surface (Fig. 1A, B). The patient did not complain of lesion-associated pain or itching. Other than the skin lesion, a physical examination revealed no other abnormality. On ultrasonography, a heterogeneous echogenic mass with internal vascularity was observed. An excisional biopsy was performed, and during excision no connection was observed between the tumor and other organs.
Fig. 1
(A, B) A 5.0×4.3 cm-sized protruding mass on the right shoulder and (C) gross features of the excised tumor.
Grossly the tumor was well-circumscribed (Fig. 1C), and histopathologic examination revealed an unencapsulated hypercellular tumor composed of a haphazard pattern of proliferating spindle cells embedded in fibrotic stroma (Fig. 2A, B). Cells were characterized by pleomorphism and a mitotic rate of 34 mitotic figures per 10 high-power fields (HPFs) (Fig. 2C). On immunohistochemical examination, tumor cells were strongly positive for CD34 and vimentin, and negative for cytokeratin, desmin, S100, and smooth muscle actin (Fig. 2D~F). These clinico-histopathologic findings were consistent with malignant SFT of the skin and the patient was transferred to our oncology department for chemotherapy.
Fig. 2
Histopathologic findings of the tumor mass. (A) The tumor was well circumscribed and unencapsulated (H&E, ×40). (B) Image showing proliferation of spindle cells in a haphazard manner (H&E, ×100). (C) Photomicrograph showing mitotic activity and cellular atypia (H&E, ×400). The tumor cells were strongly positive for (D) CD34 (×200) and (E) vimentin (×200), and negative for (F) S100 (×200).
Although SFT is a spindle cell tumor which were initially described as pleural tumors, and most involve visceral pleura, though extrapleural involvement has been well described3. SFT is a type of spindle cell tumor, and cutaneous SFT is extremely rare. Cutaneous SFT has been described as a superficial, painless mass often misdiagnosed as a lipoma or epidermal cyst clinically. Histologically, SFT is classified as storiform, herring-bone, hemangiopericytic, neural-type palisading, or diffuse sclerosing, and the spindle cells of SFTs exhibited “patternless” proliferation with thick collagen bundles arranged in the stroma4.The varied histologic features of SFT can generate a broad histologic differential diagnoses, which include dermatofibroma, dermatofibrosarcoma protuberans, smooth muscle tumors, spindle cell lipoma, hemangiopericytoma, benign peripheral nerve sheath tumors, melanoma, and cutaneous myofibroma. Immunohistochemical studies are helpful because SFTs are typically reactive for CD34 and vimentin, but not for cytokeratins, smooth muscle actin, CD31, S100, and CD685.Most SFTs are clinically benign, but approximately 5%~10% show local recurrence and/or metastasis2. Although the histologic criteria for malignant SFTs are controversial, tumor size >5 cm, dense cellularity, infiltrative growth, pleomorphism, mitotic indices >4 per 10 HPFs, and necrosis are generally considered worrisome. In the current case, the tumor showed all of these features. Histopathologically malignant SFT is extremely rare, and to date, only one report on histopathologically malignant SFT of the skin has been issued2. Prognosis and treatment options for cutaneous malignant SFTs remain uncertain, therefore, further clinicopathologic studies are required on more cases with longer clinical follow ups.
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