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

## TL;DR

A rare case of a subcutaneous tumor called ossifying fibromyxoid tumor is reported, emphasizing its importance in dermatology due to potential recurrence and metastasis.

## Contribution

This case report adds to the limited literature on OFMT by highlighting its presentation in a dermatology setting and diagnostic challenges.

## Key findings

- OFMT presented as a subcutaneous mass on the back with a delayed diagnosis requiring a second opinion.
- Histopathology showed cellular spindle cells with low mitotic index and variable S100 positivity.
- The case underscores the need for OFMT to be included in the differential diagnosis of subcutaneous masses.

## Abstract

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.