# MS-stable/TMB-high pleomorphic liposarcoma successfully treated with pembrolizumab: a case report

## TL;DR

A rare aggressive liposarcoma case was successfully treated with pembrolizumab after showing high tumor mutation burden.

## Contribution

Demonstrates successful ICI treatment in a TMB-high pleomorphic liposarcoma case with MS-stable status.

## Key findings

- Pembrolizumab significantly reduced liver metastases in a TMB-high PLPS patient.
- MS-stable/TMB-high PLPS can respond to anti-PD-1 inhibitors despite limited prior evidence.
- TMB-high may serve as a predictive biomarker for ICI response in sarcomas.

## Abstract

Pleomorphic liposarcoma (PLPS) is a rare and aggressive subtype of liposarcoma with limited treatment options. Despite studies on immune checkpoint inhibitors (ICIs) in sarcomas, there have been few reports involving PLPS. Furthermore, the significance of tumor mutation burden (TMB)-high, a known biomarker for ICIs in various solid tumors, remains unclear in sarcomas. Herein, we report the case of a 41-year-old man with postoperative liver metastasis of microsatellite (MS)-stable/TMB-high PLPS who achieved successful remission with pembrolizumab, an anti-programmed cell death protein 1 inhibitor. Initially, the patient underwent extensive resection for primary PLPS in the distal left thigh. The diagnosis of lung metastases 3 months after prompted five courses of doxorubicin and ifosfamide, resulting in stable disease. Subsequent thoracoscopic pulmonary metastasectomy allowed surgical removal of the lung metastases. However, multiple liver metastases developed 9 months following the primary extensive resection. Cancer genome profiling revealed a mutation in MSH6, MS-stable status, and a high TMB of 14.5/Mb. Pembrolizumab was initiated for a total of 35 courses at 10 months postoperatively, significantly reducing liver metastases. These findings suggest the potential of TMB-high as a predictor of ICI response in sarcomas.