Abstract
In this study, we reported an additional genetically confirmed case of renal cell carcinomas (RCCs) with t(6;11)(p21;q12) showing an unusual histological pattern. Histologically, the tumor was entirely composed of small to intermediate sized tubules and cysts. The tubules and cysts were lined by a single layer of flat, hobnail, cuboidal to columnar epithelial cells. Most cells demonstrated abundant eosinophilic cytoplasm with regular, round or oval nuclei and some inconspicuous nucleoli. All these morphological features are suggestive of tubulocystic carcinoma of the kidney. However, the tumor demonstrated moderately (2+) or strongly (3+) positive staining for TFEB, Cathepsin K, Ksp-cadherin, and vimentin but negative for TFE3, CD10, HMB45, melan A, CKpan, and CK7. Using a recently developed TFEB split FISH assay, the presence of TFEB rearrangement was demonstrated. Our results support the clinical application of a TFEB break-apart FISH assay for diagnosis and confirmation of TFEB RCC and further expand the morphologic spectrum that may be present in these neoplasms, sometimes raising a challenging differential diagnosis with other renal tumors.