Low Fluorodeoxyglucose Uptake in the Metastatic Lung Tumor From Clear Cell Renal Cell Carcinoma

A 78-year-old man had undergone laparoscopic left nephrectomy for clear cell renal cell carcinoma (CCRCC) and, three years later, partial resection for a lung metastasis of CCRCC. Follow-up computed tomography (CT) again showed a solitary oval lung nodule that was adjacent to the pulmonary vein, leading to careful CT follow-up without trans-bronchial lung biopsy. The lung nodule grew rapidly from 18 mm to 25 mm in a year. However, positron emission tomography showed only a slight increase in the maximal standardized uptake value (SUV max) of 3.76 g/mL. Under the tentative diagnosis of a metastatic lung tumor from CCRCC, the patient underwent lung wedge resection for the presumed lung metastasis. A postoperative pathological study showed a well-circumscribed oval tumor consisting of atypical cells with clear cytoplasm and densely growing in an expansive manner. Immunostaining using paraffin-embedded tissue showed that lipid droplets were observed on the tumor cells and periodic-acid Schiff (PAS)-positive granules were confirmed in the cytoplasm of the atypical cells. Oncologists should note that the SUV max value of metastatic lung tumors from CCRCC is ostensibly low due to the presence of intracytoplasmic lipids and glycogen.