AUTHOR=Miwa Satoshi , Kobayashi Hiroshi , Hirai Toshihide , Okajima Koichi , Ishibashi Yuki , Tsuda Yusuke , Zhang Liuzhe , Ando Toshihiko , Shinozaki-Ushiku Aya , Tanaka Sakae 

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

JOURNAL=Frontiers in Oncology

VOLUME=Volume 15 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2025.1552411

DOI=10.3389/fonc.2025.1552411

ISSN=2234-943X

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.