A case of adrenal undifferentiated pleomorphic sarcoma with tertiary lymphoid structures responded to pembrolizumab

INTRODUCTION: Although undifferentiated pleomorphic sarcomas are aggressive, a subset of these tumors are immunogenic and may respond to immunotherapy. CASE PRESENTATION: A 69‐year‐old man developed bilateral adrenal tumors and underwent bilateral adrenalectomy. Pathological examination revealed undifferentiated pleomorphic sarcoma harboring tertiary lymphoid structures and infiltration of CD8(+) T cells. Genome profiling revealed PD‐L1 amplification, microsatellite instability, and a high tumor mutation burden. He developed local recurrence and multiple peritoneal dissemination 2 months after surgery; adriamycin chemotherapy was ineffective for these lesions. Sustained complete remission of all lesions was achieved by administering pembrolizumab. CONCLUSION: Immunohistochemical analysis focusing on tertiary lymphoid structures and genome profiling to evaluate microsatellite instability and tumor mutation burden are essential for precision medicine and informed clinical decision‐making when treating advanced undifferentiated pleomorphic sarcoma.