6p.21 translocation renal cell carcinoma in the elderly: radiological findings mimicking fat poor angiomyolipoma or papillary renal cell carcinoma.

6p21 translocation renal cell carcinoma (RCC) harboring TFEB gene fusion is a newly classified microphthalmia-associated transcription (MiT) factor-family translocation RCC with early onset. We present a case of 78-year-old man with a 6p21 translocation RCC that was diagnosed after partial nephrectomy for an incidental renal tumor on computed tomography (CT). Unenhanced CT showed a 20 mm, mildly low-density mass in the right kidney. Contrast-enhanced CT showed a heterogeneous and prolonged, mild enhancement in the tumor. On magnetic resonance imaging, the tumor showed iso-intensity within the renal parenchyma on T1-weighted-imaging (WI), low intensity on T2WI, and no restricted diffusion with low signal on diffusion-weighted imaging, with no clear tumor pseudocapsule. Fat poor angiomyolipoma and non-clear cell RCC were listed as differential diagnoses. Robot-assisted partial nephrectomy was successfully performed. Fluorescence in situ hybridization study of the resected tumor confirmed TFEB gene break, and the patient was diagnosed with a 6p21 translocation RCC. The patient is doing well without recurrence after 2.5 years of follow-up. Our patient is the oldest patient reported in previous literature. © The Japan Society of Clinical Oncology 2021.