Surgery-enabled precision oncology in an MSI-High pulmonary artery sarcoma with Lynch syndrome: a case report.

This report describes a rare case of a vascular-origin malignant tumor (intimal sarcoma or carcinosarcoma) extending from the right pulmonary hilum along the pulmonary artery in a 44-year-old man. The patient underwent right pneumonectomy under extracorporeal membrane oxygenation (ECMO) support and achieved long-term survival through molecularly guided immunotherapy. His medical history included two early-onset colorectal cancers and a family history of malignancy, suggesting an underlying hereditary cancer syndrome. The tumor exhibited microsatellite instability-high (MSI-high) status and a high tumor mutational burden (TMB-high) with low PD-L1 expression but responded favorably to immune checkpoint inhibitors, including ipilimumab plus nivolumab and pembrolizumab, achieving sustained disease stability for over 65 months. Comprehensive genomic profiling conducted as part of a branch study later in the disease course revealed a pathogenic germline MLH1 variant, confirming the diagnosis of Lynch syndrome. This case underscores the importance of surgery-enabled precision oncology in the management of rare and aggressive tumors.