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Training Level

Resident PGY 1


Henry Ford Hospital


Background: Several variant histologic patterns of clear cell renal cell carcinoma (RCC) are well known, especially those with sarcomatoid and rhabdoid features. However, we have encountered rare cases in which a high-grade adenocarcinoma or urothelial carcinoma-like component would be difficult to appreciate as clear cell RCC. DesignWe retrieved 26 tumors with histologically typical clear cell RCC juxtaposed to a high-grade non-clear cell component.High grade non-clear cell component was defined as non-sarcomatoid, non-rhabdoid areas that would be difficult to assign as renal cell in origin if viewed in isolation. Tumors were studied with immunohistochemistry and fluorescence in situ hybridization (FISH) or sequencing.ResultsMedian percentage of poorly differentiated component: 50%(IQR20-70). All tumors showed abrupt transition from clear cell carcinoma to poorly-differentiated (non-sarcomatoid/non-rhabdoid) areas, which showed micropapillary (7/26; 27%), urothelial-like (10/26; 39%), and adenocarcinoma NOS features (9/26; 35%). 19 tumors had necrosis. Carbonic anhydrase IX (CA-IX) was uniformly positive in well-differentiated component (20/20); poorly differentiated component showed a median positivity of 82.5% (IQR 65-100). Poorly differentiated component was positive for CK7 (5/19; 26%), CK20 (3/12; 25%), AMACR (7/12; 58%), PAX8 (12/15; 80%), and showed intact FH (6/6; 100%). CDX2 was uniformly negative. Chromosome 3p loss or VHL mutation was present in 8/13 (62%), tested with either FISH (n = 9) or sequencing (n = 4). All tested cases were negative for TFE3 (0/11) and TFEB (0/9) rearrangements on FISH. 5/21 (24%) patients were alive with metastatic disease and 5/21 (24%) had died of disease on follow up. One metastasis was composed only of the poorly-differentiated component and was near-negative for CA-IX. Conclusion: Clear cell RCC with a poorly differentiated component resembling adenocarcinoma or urothelial carcinoma is a novel source of morphologic heterogeneity that has not been previously well characterized. Potential pitfalls include decreased or absent CA-IX staining the high-grade component and aberrant positivity for cytokeratin 7 or 20. With the increasing use of renal mass biopsy and biopsies of metastatic sites for targeted therapy, pathologists should be aware of this entity and consider the possibility of clear cell RCC even for morphologically unusual tumors.

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Clear Cell Renal Cell Carcinoma With a Poorly-Differentiated Component: A Novel Variant Causing Potential Diagnostic Difficulty