Clinicopathologic Study of 39 Mismatch Repair-deficient Sarcomas Demonstrates Recurrent Histologic Patterns and Supports Universal Screening of Pleomorphic Rhabdomyosarcoma, Uterine Leiomyosarcoma, and Undifferentiated and Unclassified Sarcomas

作者：Igor Odintsov, Jonathan A. Nowak, Esther Baranov, Thierry Alcindor, Candace L. Haddox, Vinayak Venkataraman, Lynette M. Sholl, Suzanne George, Leona A. Doyle, M S Redston, David Papke · 发表于：The American Journal of Surgical Pathology · 年份：2026 · DOI：10.1097/pas.0000000000002579 · 研究领域：Genetic factors in colorectal cancer、Multiple and Secondary Primary Cancers、Acute Myeloid Leukemia Research

Mismatch repair-deficient (dMMR) sarcomas are rare and incompletely characterized. Here, we studied 39 sarcomas with high microsatellite instability (MSI-H) and/or biallelic MMR gene inactivation (21 MSH2 , 9 MLH1 , 4 PMS2 , 4 MSH6 , 1 EPCAM ). All tumors evaluated with immunohistochemistry (IHC; n = 36) showed loss of MMR protein expression. Eight sarcomas were index neoplasms among the 15 patients with documented Lynch syndrome. Eighteen of 1531 sarcomas (1.2%) in our sequencing database were dMMR, with enrichment in pleomorphic rhabdomyosarcoma (PRMS; 1/5), uterine leiomyosarcoma (LMS; 7/124; 5.6%), and unclassified/undifferentiated pleomorphic sarcoma (UPS; 6/259; 2.3%). MMR IHC screening of independent cases confirmed MMR deficiency in PRMS (2/20), uterine LMS (2/20), and unclassified/UPS (1/20). Two histologic patterns were identified among unclassified/UPS. Ten tumors, designated "distinctive lobulated inflammatory sarcoma" (DLIS), showed lobular architecture, florid inflammation, and histiocytoid, variably pleomorphic neoplastic cells. All 6 patients with DLIS and follow-up (median: 6.0 y; range: 3 mo to 8.6 y) were alive with no evidence of disease (ANED), and 2 DLIS responded completely to immune checkpoint inhibition. A morphologically different group of 6 unclassified high-grade sarcomas showed sheets of epithelioid-to-rhabdoid cells with eosinophilic cytoplasm; among 5 patients with follow-up (median: 1.1 y; range: 4 mo to 6.9 y), only 1 was ANED. Surprisingly, a...