NR1D1exon6::MAML2exon2 Fusion-Positive Sarcomas: Two Additional Cases of an Emerging Soft Tissue Tumor Entity.

This article focuses on NR1D1::MAML1/2 fusion-positive sarcomas, an emerging subtype of undifferentiated soft tissue sarcomas characterized by epithelioid and spindle cell morphology. It reports two cases of NR1D1exon6::MAML2exon2 fusion-positive sarcomas confirmed by next-generation sequencing (NGS), highlighting their histopathological diversity, immunohistochemical profiles, and clinical challenges including frequent recurrence, metastasis, and poor response to chemotherapy and targeted therapies. The study emphasizes the diagnostic difficulty of these rare tumors due to their overlap with other epithelioid neoplasms and the critical role of high-throughput molecular testing for accurate diagnosis and appropriate management. Given their aggressive behavior and resistance to conventional treatments, early molecular identification is important for prognosis and therapeutic decision-making.