Non-syndromic Multifocal Low-Grade Oncocytic Renal Tumors, Including Microtumors, in End-Stage Renal Disease Kidneys with Synchronous Non-TSC Renal Cell Neoplasms

Low-grade oncocytic tumor (LOT) is a recently described indolent renal neoplasm with over 80% of tumors harboring mutations in the TSC/MTOR signaling pathway. Typically, LOTs present as sporadic solitary tumors in patients with normal renal function, and occasionally in patients with end-stage kidney disease. However, multifocal LOTs have rarely been observed in patients with tuberous sclerosis complex (TSC). We report four patients with multifocal LOTs, including microtumors, coexisting with other renal cell neoplasms in the context of chronic kidney disease (CKD) or end stage renal disease (ESRD) in the absence of clinical features of TSC. Notably, one patient had bilateral, multifocal LOTs alongside synchronous acquired cystic disease-associated renal cell carcinoma (ACD-RCC); while two other patients had concurrent clear cell papillary renal cell tumor (CCPRCT), one with multifocal and the other with solitary LOT; the remaining patient had both coexisting CCPRCT and ACD-RCC as well as multifocal LOT. This series highlights that multifocal LOTs, including microtumors, can be seen in the setting of ESRD and can arise independently of hereditary TSC. The co-occurrence with other ESRD-associated neoplasms underscores the need for broader recognition of LOT within this clinical context.