August 2020 — Genitourinary

The correct answer is Chromophobe renal cell carcinoma.

Chromophobe renal cell carcinoma (ChRCC) is the 3rd most common type of renal cell carcinomas, characterized by tumor cells with wrinkled (“koilocytic”) nuclei and distinct cell borders. The eosinophilic variant shows similar nuclear features, often accompanied by perinuclear halos. More than 85% of ChRCC show losses of chromosomes 1, 2, 6, 10, 13, 17, 21 and Y.

This tumor shows nested architecture with peripheral palisading of cells, somewhat resembling the organoid pattern that is often seen in carcinoid tumors. However, no immunohistochemical expression of chromogranin and synaptophysin was identified, excluding this possibility. Tumor morphology as well as strong positivity for both cytokeratin 7 and CD117 (C-KIT) excluded the diagnoses of oncocytoma, that is generally CK7 negative, and CD117 positive. Similarly, recently described low-grade oncocytic tumors of the kidney, that are CK7 positive/ CD117 negative were excluded. However, lack of definitive nuclear features as well as a peculiar peripheral palisading of the tumor cells made the definitive diagnosis of ChRCC challenging.

Chromosomal microarray (CMA) was performed and showed losses of chromosomes 1, 2, 6, 10, 13, 17, 21 and Y thereby supporting the diagnosis of ChRCC.

References
1. Amin MB et al: Chromophobe renal cell carcinoma: histomorphologic characteristics and evaluation of conventional pathologic prognostic parameters in 145 cases. Am J Surg Pathol. 32(12):1822-34, 2008.
2. Davis CF, Ricketts CJ, Wang M, et al. The somatic genomic landscape of chromophobe renal cell carcinoma. Cancer Cell. 2014;26(3):319-330.
3. Andeen NK, Qu X, Antic T, Tykodi SS, Fang M, Tretiakova MS. Clinical utility of chromosome genomic array testing for unclassified and advanced-stage renal cell carcinomas. Arch Pathol Lab Med. 2019;143(4):494-504.
4. Trpkov, K., Williamson, S. R., Gao, Y., Martinek, P., Cheng, L., Sangoi, A. R., Hes, O. (2019). Low-grade oncocytic tumour of kidney (CD117-negative, cytokeratin 7-positive): a distinct entity? Histopathology, 75(2), 174-184.