Inflammatory Rhabdomyoblastic Tumor With Extensive Necrosis and Overdiagnosis in Biopsy Specimens: A Rare Case Report.

Inflammatory rhabdomyoblastic tumor (IRMT) is a newly recognized type of intermediate/borderline rhabdomyogenic tumor. It most commonly occurs in the lower extremities and trunk muscles of young and middle-aged men, characterized by slow growth, clear boundaries, a fibrous capsule containing a large number of peripheral lymphocyte aggregations, morphological spindle to epithelioid cells, and dense histiocytic infiltration. It exhibits an immunohistochemical profile consistent with a primitive skeletal muscle phenotype and a near-haploid karyotype genetically, with most behaving indolently. As malignant neoplasms of skeletal muscle differentiation are more common than benign ones, IRMT cannot yet be classified into the existing subtypes of neoplasms of skeletal muscle differentiation, making it prone to misdiagnosis as other pleomorphic tumors, including being overdiagnosed as high-grade sarcomas. We present a case report of IRMT initially diagnosed as rhabdomyosarcoma based on a core needle biopsy specimen, which was overdiagnosed. Additionally, we review the literature to explore the clinicopathological features of this tumor, aiming to enhance understanding of this type of tumor.