A Case Report of Subcutaneous Ossifying Fibromyxoid Tumour of the Back.

Ossifying fibromyxoid tumour (OFMT) is a rare subcutaneous soft tissue neoplasm, with unclear lineage and intermediate differentiation. Typically presenting as a benign growth, however it can recur locally, and malignant variants have been reported. We present an unusual case of OFMT occurring as a subcutaneous mass on the right upper back. A 29-year-old gentleman presented with one-year history of a painless, slowly enlarging mass on his right upper back. He had no relevant medical history, was not on any medications, and had no family history of skin cancer. Physical examination revealed a 25mm x 25mm skin-coloured, stony-hard, well circumscribed mass. The initial clinical diagnosis was a calcified epidermoid cyst. The lesion was excised and sent for histopathology, which revealed well-circumscribed cellular spindle cells with low mitotic index. Immunohistochemistry showed variable S100 positivity. Due to its rarity, the diagnosis was delayed as the biopsy required a second opinion from a tertiary hospital. The final pathological diagnosis confirmed OFMT. This case describes the very rare presentation of OFMT in a dermatology clinic, highlighting the importance of recognising this neoplasm due to its potential for recurrence and metastasis. This unusual case of OFMT broadens the dermatological differential diagnosis for a subcutaneous mass.