Cutaneous solitary fibrous tumour with myxoid stroma.

Abstract

Sir, Solitary fibrous tumour (SFT) is a distinctive CD34‐positive spindle cell neoplasm of probable mesenchymal origin that generally arises in the pleura.1–5 Rare cases of SFT arising in the skin have recently been reported, reinforcing the notion that SFT may arise in non‐serosal sites.4, 5 We report an additional case by describing a shelled‐out lesion of SFT with abundant myxoid change. A 42‐year‐old Korean woman presented in April 1998 with an asymptomatic, slowly enlarging lesion on the thigh. The lesion was first noted 5 years previously. Examination showed a solitary, about 1‐cm diameter, well‐demarcated, skin‐coloured, round, smooth‐surfaced, non‐tender nodule on the right upper posterior thigh (Fig. 1a). Lymph nodes were not palpable. Under a clinical diagnosis of epidermal cyst, incision and tumour enucleation were performed to minimize scarring. The spindle cell tumour was located in the dermis and subcutis, and had a smooth border. It was surrounded by a thin rim of normal tissue like a pseudoencapsulation, thus making the tumour easily shelled out. There were peripheral foci of entrapped normal adipocytes (Fig. 1b). The tumour cells appeared fibroblastic, with a weakly alcianophilic, fibrillar fibromyxoid stroma, and were in a patternless swirling and focally storiform arrangement. The tumour exhibited alternating hypercellular and hypocellular areas. The tumour cells had an elongate, dendritic spindle cell morphology and the nuclei were bland (Figs 1c,d). The mucinous stroma was positive to alcian blue (Fig. 1d) and colloidal iron, but negative to periodic acid–Schiff with diastase and toluidine blue. Immunohistochemical markers for smooth muscle actin, desmin, lysozyme, CD68, S‐100 protein, epithelial membrane antigen, cytokeratin, CD117 and factor XIIIa were negative, but diffuse positivity for CD34 was characteristic (Fig. 1c). For differential diagnosis of dermatofibrosarcoma protuberans (DFSP), reverse transcription–polymerase chain reaction assay for the DFSP‐specific COL1A1‐PDGFB chimeric fusion transcripts using eight of the possible 51 break points in the COL1A1 gene was negative. SFT was a final diagnosis. Two years later, there were no recurrences.