Drs. Guido Martignoni and Anna Caliò from the University of Verona in Italy discuss their recent study on primary and metastatic fumarate hydratase (FH)-deficient renal cell carcinomas. Six metastatic tumors were histologically documented with high frequency of involvement of lymph nodes, liver and peritoneal cavity. Metastases were morphologically heterogeneous often differing from corresponding primary. Interestingly, some peritoneal metastases morphologically resembled a benign reactive mesothelial process or primary peritoneal mesothelioma, a pitfall that can be avoided by performing IHC panels that include PAX8 and FH. As for therapeutic predictors, significant PD-L1 labeling was found in 60% of primary renal tumors, whereas none of them carried pathogenetic EGFR mutations.