Chromophobe renal cell carcinoma, oncocytic variant: a proposal of a new variant giving a critical diagnostic pitfall in diagnosing renal oncocytic tumors

Abstract

In chromophobe renal cell carcinoma (RCC), two forms of typical and eosinophilic variants have been reported to date. We have previously reported a new variant of chromophobe RCC, namely an oncocytic variant. However, little is known on the histological features of this variant. In this article, we report such five cases. Macroscopically, the tumor was well demarcated, but unencapsulated. The cut surface of the tumor showed brown in color, but neither hemorrhage nor necrosis was seen. Microscopically, the tumor consisted of predominant tubular configuration with or without various proportion of solid-sheet pattern. In one tumor, tumor cells microscopically invaded branches of renal vein. In addition, the constituting cells were characterized by the oncocytic cytoplasm, trivial to minimal variation in tumor size, indistinct to slightly distinct cell border, centrally located round nuclei and the absence of perinuclear halo. These characteristics entirely resembled renal oncocytoma. However, neoplastic cells immunohistochemically showed the diffuse and strong labeling for cytokeratin 7 and mitochondrial antigen in all cases. In addition, in fluorescence in situ hybridization (FISH) study the loss of more than four chromosomes among chromosomes 7, 10, 13, 17 and 21 was confirmed in all tumors and the diagnosis of chromophobe RCC was rendered. In conclusion, we propose a new variant, namely an oncocytic variant, of chromophobe RCC morphologically resembling renal oncocytoma and biologically showing characteristics of chromophobe RCC, and this recognition is practically crucial in the differential diagnosis from renal oncocytoma.

New and emerging renal entities: a perspective post‐WHO 2016 classification

“…In our view, these tumours show morphological similarities to the four cases included in the study by Davis et al ., which were labelled ‘eosinophilic chromophobe RCC’ and showed an absence of any copy number alterations; an immunohistochemical profile was not provided for these cases . The only other study that included remarkably similar tumours was by Kuroda et al ., who described five cases designated ‘chromophobe RCC, oncocytic variant’ that strongly resembled renal oncocytomas, but were CD117‐negative and diffusely CK7‐positive, and, on FISH, showed multiple (at least four) chromosomal losses of chromosomes 7, 10, 13, 17, and 21 …”

Differentiation of oncocytoma from chromophobe renal cell carcinoma (RCC): can novel molecular biomarkers help solve an old problem?

“…Despite having some subtle distinguishing macroscopic, microscopic and ultrastructural differences, there is often need to use ancillary histochemical and immunohistochemical (IHC) stains to differentiate these two entities. Recently, a new oncocytic variant of a chRCC was described, that morphologically resembles RO, but has the biological characteristics of a chRCC 43. This further adds to the difficulties for pathologists to discern ROs from all these variants of chRCCs.…”

Low‐grade oncocytic tumour of kidney (CD117‐negative, cytokeratin 7‐positive): a distinct entity?

“…Although these tumours show overlapping morphological features with oncocytoma and eosinophilic ChrRCC, they do not fit completely into either of these entities, based on the morphology and the immunoprofile. To our knowledge, this type of oncocytic tumour with low‐grade features is not well characterised in the literature …”