# Resurfacing Threats: Metastatic Ossifying Fibromyxoid Tumor Emerging After Almost Two Decades

## TL;DR

A rare tumor called ossifying fibromyxoid tumor (OFMT) showed late metastases 19 years after initial surgery, highlighting the need for long-term monitoring.

## Contribution

This case report highlights the unexpected metastatic potential of a typical OFMT despite no initial signs of malignancy.

## Key findings

- The patient developed multiple metastases 19 years after initial diagnosis of a non-malignant OFMT.
- RNA sequencing and DNA methylation profiling confirmed the metastases were the same tumor entity.
- A potential fourth lesion was detected, emphasizing the unpredictable nature of OFMT progression.

## Abstract

Ossifying fibromyxoid tumor (OFMT) is an extremely rare mesenchymal tumor of uncertain differentiation having a potential for local recurrences and metastasis. OFMT can be classified as typical, atypical, and malignant tumors based on nuclear grade, cellularity, and mitotic rate. However, predicting the biological behavior remains challenging. We report one of these challenging cases of OFMT with metastases after 19 years. The primary tumor did not show morphologic characteristics of malignancy. We performed targeted RNA sequencing, copy number variation (CNV) analysis on all lesions and additional DNA methylation profiling.

Herein we report the case of a 66‐year‐old Caucasian female patient diagnosed in 2004 with an OFMT on her back that was surgically removed. In August 2023, the patient presented with two new soft tissue lesions in the right lower thigh and left gluteal area. Biopsy has been performed on both lesions. Pathology reports demonstrated an OFMT with an EP400:PHF1 fusion. Both tumors were confirmed to represent the identical entity. Surgical removal of both tumors was performed with clear margins. The presence of late sequential metastases 19 years after initial resection of an OFMT, without any signs of malignancy after pathology review of the 2004 lesion was suggested. In December 2023, a potential fourth similar mass was detected with MRI and a full body PET‐CT within the distal left semimembranosus muscle. A biopsy of this lesion has not been performed yet. It is currently being closely monitored through regular MRI examinations with contrast agents at intervals of 3 months.

This case demonstrates the rare unpredictable potential of even typical OFMT to develop multiple soft tissue metastases after 19 years. Therefore, clinicians need to be aware of the metastatic potential of this tumor. Comprehensive and prolonged postoperative follow‐up is necessary to track local recurrences and metastases.