Abstract
RATIONALE: Low-grade oncocytic tumor (LOT) is characterized by cells with oncocytic/eosinophilic cytoplasm. Despite the clear definition of the tumor, challenges persist as some tumors resemble LOT, complicating the diagnosis. Therefore, understanding its characteristics is crucial for accurate diagnosis and differentiation from other renal oncocytic tumors. PATIENT CONCERNS: An 81-year-old woman was incidentally found to have a right renal mass during routine examination. DIAGNOSES: Histological examination of the specimen obtained from a partial nephrectomy revealed oncocytic cells with abundant eosinophilic granular cytoplasm, indistinct cell borders, uniform round nuclei, and inconspicuous nucleoli, arranged in small nesting and trabecular patterns. A vague peri-nuclear halo was also observed. Immunohistochemistry demonstrated significant positivity for CK7, while CD117, CA9, GATA3, CK20, RCC, and GPNMB were negative. Based on these findings, we diagnosed the tumor as a LOT. INTERVENTIONS: The patient underwent partial nephrectomy for tumor removal. OUTCOMES: There was no evidence of recurrence or metastasis during follow-up. LESSONS: LOT can exhibit variations in its immunohistochemical profile. Therefore, additional studies and the accumulation of similar cases are necessary.