Reappraisal of Morphological Differences between Renal Medullary Carcinoma, Collecting Duct Carcinoma, and Fumarate Hydratase-Deficient Renal Cell Carcinoma

Renal medullary carcinomas (RMCs) and collecting duct carcinomas (CDCs) are rare subsets of lethal high-stage, high-grade distal nephron-related adenocarcinomas with a predilection for the renal medullary region. Recent findings have established an emerging group of fumarate hydratase (FH)-deficient tumors related to hereditary leiomyomatosis and renal cell carcinoma (HLRCC-RCCs) syndrome within this morphologic spectrum. Recently developed, reliable ancillary testing has enabled consistent separation between these tumor types. Here, we present the clinicopathologic features and differences in the morphologic patterns between RMC, CDC, and FH-deficient RCC in consequence of these recent developments. This study included a total of 100 cases classified using contemporary criteria and ancillary tests. Thirty-three RMCs (SMARCB1/INI1-deficient, hemoglobinopathy), 38 CDCs (SMARCB1/INI1-retained), and 29 RCCs defined by the FH-deficient phenotype (FH/2SC or FH/2SC with FH mutation, regardless of HLRCC syndromic stigmata/history) were selected. The spectrum of morphologic patterns was critically evaluated, and the differences between the morphologic patterns present in the 3 groups were analyzed statistically. Twenty-five percent of cases initially diagnosed as CDC were reclassified as FH-deficient RCC on the basis of our contemporary diagnostic approach. Among the different overlapping morphologic patterns, sieve-like/cribriform and reticular/yolk sac tumor-like patterns favored RMCs, whereas intracystic papillary and tubulocystic patterns favored FH-deficient RCC. The tubulopapillary pattern favored both CDCs and FH-deficient RCCs, and the multinodular infiltrating papillary pattern favored CDCs. Infiltrating glandular and solid sheets/cords/nested patterns were not statistically different among the 3 groups. Viral inclusion-like macronucleoli, considered as a hallmark of HLRCC-RCCs, were observed significantly more frequently in FH-deficient RCCs. Despite the overlapping morphology found among these clinically aggressive infiltrating high-grade adenocarcinomas of the kidney, reproducible differences in morphology emerged between these categories after rigorous characterization. Finally, we recommend that definitive diagnosis of CDC should only be made if RMC and FH-deficient RCC are excluded

Pericytic tumors of the kidney-a clinicopathologic analysis of 17 cases

The pericytic (perivascular myoid cell) family of tumors is a distinctive group of mesenchymal neoplasms encountered in superficial sites and only rarely seen in viscera. The pericytic family subtends a spectrum of lesions, namely, glomus tumors and variants; myopericytoma, including myofibroma; and angioleiomyoma. In light of the contemporary classification of pericytic lesions, we identified and reviewed 17 cases of renal pericytic tumors from the files of 6 referral centers. These tumors presented over an age range of 17 to 76 years (mean 46.7, median 53), with essentially equal male-female ratio. History of hypertension (available in 11 patients) was noted in 7 (64%), which persisted even after surgical resection, including in 2 younger patients (17 and 30 years). The tumors (1.7-11.0 cm) included glomus tumors (n=11); glomangiomyoma (n=1); glomus tumor with atypical features (n=1); and angioleiomyoma (n=1), as well as tumors showing features overlapping pericytic tumor subtypes (n=3). The histomorphology observed in these renal examples closely resembled that of their soft tissue counterparts, a subset with symplastic changes and atypical features, and pericytic immunophenotype. Despite large size and deep site, no progression was identified during a median of 7 months follow-up (1-62 months). In context of prior reported experience, our series identifies a wide morphologic spectrum, including lesions presenting composite morphologies. Taken with the experience of others, our series further corroborates that malignant behavior is rare, and that criteria associated with aggression among soft tissue pericytic tumors may not be predictive for those in the kidney