Microscopic description:

IHC: Tumor positive for CK7 and PAX8; while negative for CAIX and CD117.

Oncocytic cells with eosinophilic cytoplasm, round to oval nuclei, and occasional inconspicuous nucleoli (IUSP grade 1-2). Cells lack irregularities and show focal perinuclear halos.

Cells arranged in solid sheets and compact nests.

Tumor is sharply demarcated from the surrounding parenchyma.

Based on the histopathological features and IHC stains, the tumor shows features consistent with a low-grade oncocytic tumor of the kidney.

Discussion:

Low-Grade Oncocytic Tumors (LOT) are a recently proposed emerging renal entity. They are often relatively small single tumors.

Rarely, LOT have been found in patients with Tuberous Sclerosis Complex.

LOT are typically benign and shares histological characteristics of both renal oncocytomas and eosinophilic chromophobe renal cell carcinoma.

Table of IHC stains used

LOT are usually discovered incidentally and have a slightly increased prevalence in females (1:1.3).  LOT also have a broad age range. (10 – 87 years old)

IHC of LOT show positive reactivity for CK 7 and PAX8 and absent expression for CD117. IHC of an Oncocytoma exhibits scattered CK7 positive cells and diffuse CD117 reactivity. Eosinophilic chromophobe renal cell carcinoma shows diffuse staining for both CK7 and CD117.

References:

Athanazio, D.A., Amorim, L.S., da Cunha, I.W. et al. Classification of renal cell tumors – current concepts and use of ancillary tests: recommendations of the Brazilian Society of Pathology. Surg Exp Pathol 4, 4 (2021). https://doi.org/10.1186/s42047-020-00084-x

Hes O, Trpkov K. Do we need an updated classification of oncocytic renal tumors? : Emergence of low-grade oncocytic tumor (LOT) and eosinophilic vacuolated tumor (EVT) as novel renal entities. Mod Pathol. 2022 Sep;35(9):1140-1150. doi: 10.1038/s41379-022-01057-z. Epub 2022 Mar 10. PMID: 35273336.

Mansoor M, Siadat F, Trpkov K. Low-grade oncocytic tumor (LOT) - a new renal entity ready for a prime time: An updated review. Histol Histopathol. 2022 May;37(5):405-413. doi: 10.14670/HH-18-435. Epub 2022 Feb 14. PMID: 35156688.

Trpkov, K, Williamson, S R, Gao, Y, Martinek, P, Cheng, L, Sangoi, A R, Yilmaz, A, Wang, C, San Miguel Fraile, P, Perez Montiel, D M, Bulimbasić, S, Rogala, J & Hes, O (2019) Histopathology 75, 174– 184. https://doi.org/10.1111/his.13865 Low-grade oncocytic tumour of kidney (CD117-negative, cytokeratin 7-positive): a distinct entity?

Trpkov K, Williamson SR, Gill AJ, Adeniran AJ, Agaimy A, Alaghehbandan R, Amin MB, Argani P, Chen YB, Cheng L, Epstein JI, Cheville JC, Comperat E, da Cunha IW, Gordetsky JB, Gupta S, He H, Hirsch MS, Humphrey PA, Kapur P, Kojima F, Lopez JI, Maclean F, Magi-Galluzzi C, McKenney JK, Mehra R, Menon S, Netto GJ, Przybycin CG, Rao P, Rao Q, Reuter VE, Saleeb RM, Shah RB, Smith SC, Tickoo S, Tretiakova MS, True L, Verkarre V, Wobker SE, Zhou M, Hes O. Novel, emerging and provisional renal entities: The Genitourinary Pathology Society (GUPS) update on renal neoplasia. Mod Pathol. 2021 Jun;34(6):1167-1184. doi: 10.1038/s41379-021-00737-6. Epub 2021 Feb 1. Erratum in: Mod Pathol. 2021 May;34(5):1037. PMID: 33526874.

CASE IMAGES