Malignant solitary fibrous tumor in the subcutis: Report of a rare superficial malignant type and review of published work

Abstract

An 82‐year‐old Japanese man presented with a 90 mm × 80 mm subcutaneous nodule on the left chest, not connected to the pleura, described as hypointense on T₁‐weighted magnetic resonance imaging. Histologically, a well‐demarcated nodule demonstrated a patternless pattern composed of hemangiopericytoma‐like and short storiform patterns from the subcutis into deeper tissue. Antler‐like branching blood vessels and keloidal‐type collagen bundles were seen. Myxoid change was seen in hypocellular areas. Bizarre cells and multinucleated giant cells could be easily identified. Approximately 5 mitoses per 10 high‐power fields could be detected. The majority of proliferating spindle cells were positive for CD34, CD99 and BCL2 expression. Signal transducer and activator of transcription (STAT)6 was strongly expressed in the nuclei. The Ki‐67 proliferation index was 60%. We performed wide local excision with a 30‐mm margin, along with resection of intercostal muscles, fasciae and periostea. Neither local recurrence nor distant metastases have occurred in 16 months of follow up. The present case is consistent with malignant solitary fibrous tumor in the subcutis histologically mimicking myxofibrosarcoma or undifferentiated pleomorphic sarcoma, definitively diagnosed by immunoexpression of STAT6. We performed a review of the published work and identified six previously reported patients with malignant superficial solitary fibrous tumor to validate the characteristics of this rare type. Four men and two women were included. The sarcomas involved the head area, trunk and thigh. Only one tumor‐associated death occurred despite excision and radiotherapy. Complete excision is a possible treatment choice for this tumor type.

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