COW-2021-11

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1. Low-grade oncocytic tumor of kidney (LOT)

This needle biopsy shows an oncocytic renal neoplasm with features of low-grade oncocytic tumor of kidney (LOT) occupying the entire length of one of the renal biopsy cores. At low magnification, the tumor showed compact, focal tubulo-reticular, and tubular growth. At high magnification, the tumor cells displayed solid to nested and compact acinar growth. The tumor cells demonstrated oncocytic cytoplasm, uniformly round to oval nuclei, with no evidence of nuclear irregularities. Focally, tumor cell nuclei exhibited delicate perinuclear halos or clearing. No nuclear pleomorphism, multinucleation or mitotic activity were identified. Coagulative necrosis was absent.

The tumor cells expressed diffuse cytoplasmic staining with CK-7, CK AE1/AE3, and diffuse nuclear staining with PAX-8. No staining was present with CD117, AMACR, and CA-IX. Scattered tumor cells were positive with CD10.

Low-grade oncocytic tumor of kidney has been recently described as a distinct entity and not currently included in the WHO classification. This tumor demonstrates solid and compact nested growth pattern. The tumor cells display oncocytic cytoplasm with focal perinuclear clearing or halos, and uniformly round to oval nuclei, but without significant atypia. Diffusely positive CK-7 and negative CD117 immunoreactivity are present in all reported cases. In addition, uniform positive staining was found for CK AE1-AE3 and PAX8. The main differential diagnosis for LOT includes oncocytoma and eosinophilic variant of chromophobe renal cell carcinoma (Chr RCC). The cells of oncocytoma are usually diffusely positive for CD117 and negative for CK7, and the cells of Chr RCC are diffusely positive for both markers.

Low-grade oncoytic tumor of kidney is usually a small and single tumor, and occurring in patients with a mean age of 66 with a female predilection. Reportedly, their behavior is indolent. In their series with 28 cases with a mean follow up of 31.8 months, Trpkov et al, found no disease progression. It is important to recognize and entertain this entity in the differential diagnoses of incidental renal neoplasms in needle biopsies of kidney performed for medical diseases.

1. Trpkov K, Williamson S, Gao Y, et al. Low-grade oncocytic tumor of kidney (CD117-negative, cytokeratin 7-positive): a distinct entity? Histopathology 2019, 74:31-59.

2. Siadat F, Trpkov K. ESC, ALK, HOT and LOT: Three letter acronyms of emerging renal entities knocking on the door of the WHO classification. Cancers 2020, 12 (168).

3. Trpkov K, Williamson SR, Gill AJ, et al. Novel, emerging and provisional renal entities: The genitourinary pathology society (GUPS) update on renal neoplasia. Mod Pathol 2021 Feb 1. Doi: 10.1038/s41379-021. Online ahead of print.

Neriman Gokden
University of Arkansas for Medical Sciences
Little Rock, AR
Email: gokdenneriman@uams.edu

Kidney

Kidney, low-grade oncocytic tumor, biopsy.