Molecularly defined renal cell carcinomas: practical approaches for surgical pathologists.

Molecularly defined renal carcinomas (MDRC) represent a heterogeneous group of tumours characterized by disease-defining genetic alterations, and the documentation of these mutations is necessary for their diagnosis. This group includes TFE3-rearranged renal cell carcinoma (RCC), TFEB-rearranged RCC, TFEB-amplified RCC, fumarate hydratase (FH)-deficient RCC, succinate dehydrogenase (SDH)-deficient RCC, SMARCB1-deficient renal medullary carcinoma (RMC), ALK-rearranged RCC, and ELOC-mutated RCC. Although they account for only about 5% of RCC, they are clinically significant due to distinctive biology, frequent diagnostic pitfalls, and therapeutic implications. Many pathology laboratories lack immediate access to fluorescence in situ hybridization (FISH) or next-generation sequencing (NGS) to confirm MDRC; this review emphasizes morphologic recognition and immunohistochemical surrogates, followed by rational triage for ancillary testing when available.