Perineal mass in a 50-year-old man

A man in his fifties presented with a lump in his left anal/perineal region, which was clinically thought to be a lipoma and was excised. No preoperative imaging was available. Review the high-quality, interactive digital Aperio slide at http://virtualacp.com/JCPCases/jclinpath-2019-206337/ and consider your diagnosis. 1. Epithelioid angiosarcoma (EAS). 2. Epithelioid malignant peripheral nerve sheath tumour (eMPNST). 3. Malignant rhabdoid tumour (MRT). 4. Melanoma. 5. Proximal epithelioid sarcoma (ES). 6. Pseudomyogenic haemangioendothelioma (PH). The correct answer is after the Discussion. The diagnosis in this case is proximal ES. This was based on the following morphological features and immunohistochemistry. The sections show a cellular tumour composed of large polygonal cells with vesicular nuclei with prominent nucleoli and abundant eosinophilic granular cytoplasm (figure 1A). There are 8 mitoses per 10 high-power fields and focal necrosis. The tumour grows in sheets to form large nodules with a mild intratumoural lymphoid population and infiltrates into the surrounding fibroadipose tissue. The morphology and the immunohistochemistry findings are in keeping with proximal-variant epithelioid sarcoma (PES). The tumour shows strong and diffuse expression of epithelial membrane antigen (EMA) and CD34, with patchy expression of AE1/AE3 (figure 1B,C). There is also loss of nuclear expression of INI1 (figure 1D). There is no expression of MNF116, CAM5.2, S100 protein, CD30, CD31, FLI1, ERG, SOX10, HMB45, MelanA, desmin, smooth muscle actin (SMA), myogenin, CD45, PLAP or prostate-specific antigen. Figure 1 Scanned virtual slide (proximal-type ES). Proximal-type ES. (A) The tumour is composed of sheets and nests of relatively large and monomorphic epithelioid cells with vesicular nuclei and prominent nucleoli. (B,C) There is diffuse and strong expression of CD34 (B) and epithelial …