Chemotherapy with bevacizumab and pembrolizumab followed by radiotherapy for unclassified round cell sarcomas of the gallbladder: A case report and review of literature.

Unclassified round cell sarcomas (URCS) are a rare sarcoma subtype. Systemic treatment options for advanced URCS are limited, primarily consisting of radiotherapy and chemotherapy, while the efficacy and prerequisites for immunotherapy in URCS remain unclear. A better understanding of factors influencing the response to immunotherapy in URCS may facilitate the development of combination treatment strategies to prolong patient survival. This study reports a 60-year-old male patient with gallbladder URCS who was administered a combination of chemotherapy, bevacizumab, and pembrolizumab, followed by radiotherapy, achieving a progression-free survival of 11 months. This result supports the potential application of immunotherapy in advanced URCS. The patient exhibited vascular endothelial growth factor receptor amplification, mutations in CHEK1, ERCC3, and TP53, deletion of CD274 (gene of PD-L1), and microsatellite stability. These findings suggest that immunotherapy may be beneficial to URCS patients with low PD-L1 expression and microsatellite stability, when accompanied by immunotherapy-associated genetic alterations.