Rare case of atypical ossifying fibromyxoid tumour of soft tissue in anterior mediastinum: a case report

Purpose We report a rare case of large atypical ossifying fibromyxoid tumour (OFMT) in an unusual site, the anterior mediastinum, in a 51-year-old female. Methods The tumour was fixed in 10% neutral-buffered formalin, embedded in paraffin, and cut sections stained in haematoxylin-eosin. Immunohistochemistry for variety of tumour markers were performed. Results Histopathology revealed a tumour surrounded by thick fibrous pseudo-capsule, paucicellular fibrous septae extending inwards and tumour lobules containing variably cellular arrangement of plump epithelioid cells with ovoid nuclei and inconspicuous eosinophilic cytoplasm, surrounded by fibromyxoid stroma. Tiny areas of metaplastic bone were present in fibrous septae. Scattered areas of necrosis and mitosis up to 3 per 10 high power fields (hpf) were noticed. Tumour cells were positive for vimentin, S-100 and NSE, showed scattered nuclear positivity for AE1/3 and were negative for EMA, actin, desmin, GFAP, Melan-A, CD34, CD21 and CD57. Discussion OFMT is a rare neoplasm of uncertain lineage, commonly arising in extremities, trunk, head and neck, oral cavity and rarely in retroperitoneum and mediastinum. 1–6 Few have atypical or malignant features, designated atypical or malignant OFMT and are characterised by a combination of hypercellularity, high nuclear grade, increased mitosis of more than 2 per 50 hpf and necrosis. 1–5