A case report of a low-grade oncocytic tumour of kidney – a new and emerging entity

Abstract

Background: Low-grade oncocytic tumour (LOT) is an emerging entity describing a slow growing tumour with morphologic features overlapping between chromophobe renal cell carcinoma (ChRCC) and oncocytoma, staining positive for cytokeratin-7 and negative for CD117 (c-kit). This entity has been recently recognised in the WHO classification of tumours 5th edition 2022. Presentation: In this case report, we present the case of a 77-year-old lady who has a tumour in the lower pole of her right kidney, discovered incidentally during work up for recurrent urinary tract infections. Grossly, the tumour was well circumscribed with solid brown areas and haemorrhage. Microscopically, the tumour was an oncocytic neoplasm with low-grade features consisting of small nests of cells among oedematous looking stroma, large polygonal cells with eosinophilic cytoplasm, occasional binucleate cells, and cells with perinuclear halos. Immunohistochemically, the neoplasm was strongly diffusely positive for cytokeratin-7, and negative for CD117. This diagnosis is consistent with LOT and has a favourable outcome for the patient. Conclusion: LOT has overlapping morphological feature with other oncocytic renal neoplasms for example ChRCC and oncocytoma, however has a distinct immunohistochemistry profile. It is thus important to be considered as part of a differential diagnosis given its indolent nature that can impact a patient’s management.