Primary Renal Mesenchymal Tumors: A Study from North India, Emphasizing Rare Entities and Molecular Profiles.

Primary renal mesenchymal tumors (PRMT) are uncommon, heterogeneous, and diagnostically challenging neoplasms. Comprehensive institutional data on the prevalence, clinicopathological features, immunohistochemical and molecular profiling, and outcomes of PRMTs in South Asia are limited. This retrospective study analyzed 64 surgically resected PRMTs from 1975 nephrectomies performed at our institution between January 2014 and June 2024. Tumors were categorized according to the World Health Organization (WHO) 2022 classification system. Clinico-radiological and histopathological, treatment and follow-up data were retrieved from the hospital information systems. Among all surgical nephrectomies, 64 PRMTs were identified (prevalence 3.2%). According to the WHO 2022 classification, 37 tumors (58%) were benign, 22 (34%) were malignant, and 5 tumors (8%) were intermediate. The overall female-to-male ratio was 1.1:1. Adults comprised 81.2% of the patients (n = 52), children comprised 18.8% (n = 12). Angiomyolipoma was the most common tumor, comprising 56% of PRMTs (n = 36), followed by clear cell sarcoma of the kidney (n = 7; 11%), Ewing sarcoma (n = 6; 9%), leiomyosarcoma (n = 6; 9%), congenital mesoblastic nephroma (n = 3; 5%), and other rare entities. The mean follow-up duration was 41.6 months, with recurrence in three cases and metastasis in six cases. This is one of the largest Indian series conducted on PRMTs, documenting a diverse spectrum. Malignant tumors tend to occur at a younger age, although exceptions have been reported. The occurrence of extremely rare entities highlights the critical role of immunohistochemistry and molecular testing in the accurate classification and treatment planning of these tumors.