# BRAFV600E Metastatic Synovial Sarcoma Treated with BRAF & MEK Inhibitors Achieves Complete Response. A Case Report & Literature Review

## TL;DR

A rare case of BRAFV600E synovial sarcoma achieved complete response with BRAF and MEK inhibitors, but also developed a rare adverse event.

## Contribution

First case of BRAFV600E synovial sarcoma with complete pathological and radiological response to BRAF and MEK inhibitors.

## Key findings

- BRAFV600E synovial sarcoma showed complete pathological response after treatment with BRAF and MEK inhibitors.
- Local recurrence was managed with resumption of inhibitors and radiotherapy, resulting in complete radiological response.
- Hemophagocytic lymphohistiocytosis occurred as a rare adverse event and resolved with corticosteroids.

## Abstract

—Synovial sarcoma is a rare soft tissue sarcoma. Treatment of synovial sarcoma includes surgery, radiation, pazopanib, and chemotherapy. Targeted therapies, such as B-Raf proto-oncogene, serine/threonine kinase (BRAF) inhibitors, are emerging as a potential treatment option. We describe the sixth case of a BRAFV600E synovial sarcoma, the first extra-thoracic case. This case is the first to show a complete pathological response to BRAF & mitogen-activated protein kinase kinase (MEK) inhibitors.

—We treated a 22-year-old male with a left groin BRAFV600E synovial sarcoma with doxorubicin, Ifosphamide & Sodium 2-Mercaptoethanesulfonate. When we identified BRAFV600E in the tumor, the BRAFV600E and MEK inhibitors (dabrafenib & trametinib) were initiated, followed by surgery, with a complete pathological response. Nine months after the surgery, a local recurrence prompted the resumption of dabrafenib & trametinib followed by radiotherapy, resulting in complete radiological response and the development of hemophagocytic lymphohistiocytosis treated with corticosteroids with resolution of symptoms.

—Panel sequencing of synovial sarcoma can identify targetable mutations. Treatment of BRAFV600E synovial sarcoma with dabrafenib & trametinib can lead to complete pathological response and prolonged radiological response, as well as the rare adverse event of hemophagocytic lymphohistiocytosis. Prospective clinical trials are needed to evaluate the efficacy and safety of BRAFV600E & MEK inhibitors as a therapeutic approach in BRAFV600E synovial sarcoma.