18 F-FDG-avid Renal Oncocytoma in a Breast Cancer Patient: A Diagnostic Pitfall on PET/CT

Oncocytoma is a benign renal tumor, composed of oncocytic cells that are rich in mitochondria. Despite being benign, oncocytomas may show increased uptake on 18 F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT), which can lead to false-positive interpretations. We report the case of a 66-year-old female with breast cancer presented with a huge left breast mass with matted axillary lymph nodes referred for 18 F-FDG PET/CT for staging. 18 F-FDG PET/CT show large hypermetabolic fungating lobulated mass in the outer quadrant of left breast (primary tumor) and 18 F-FDG avid ipsilateral metastatic left axillary and left internal lymph nodes. In addition, a large 18 F-FDG avid right renal mass is noted. Finding is suspicious for renal primary versus metastatic. Biopsy showed oncocytoma. Renal oncocytomas may show moderate-to-intense 18 F-FDG uptake, which is typically associated with malignant lesions, leading to diagnostic confusion. 18 F-FDG avid renal lesions must be interpreted cautiously. Multimodality imaging and histopathological correlation remains the gold standard.