Skeletal metastases from renal cell carcinoma: diagnostic uncertainty with molecular imaging.

DESCRIPTION A 54-year-old patient underwent right radical nephrectomy for what was then diagnosed as a Stage-II (T2bN0M0) renal cell carcinoma (RCC). Four months after surgery, the patient reported of pelvic pain and had a rising serum alkaline-phosphatase level. The tecnetium-99 mmethylene-diphosphate (Tc99m-MDP) bone scan then demonstrated a focus of uptake in the right ischium, corresponding to the locus of pain (figure 1). As part of further metastatic work-up, a whole body F-fluorodeoxyglucose positron-emission tomography (FDG-PET) scan was performed; this however could not demonstrate any anomalies (figure 2). Six months after surgery (2 months after the first scan) the patient complained of generalised bony pains. Then, metastatic disease was confirmed when reimaging (with chest radiograph and a repeat bone scan) showed pulmonary and vertebral metastases (figure 3). Two commonly used molecular-imaging techniques in the general evaluation of skeletal metastases are the bone scan and the FDG-PET scan. Whereas the bone scan is dependent on bone turnover, the FDG-PET scan depends on increased glucose uptake by cancerous cells, often accompanied by upregulated glucose transporter 1 (GLUT-1) expression. With RCC, however, FDG-PET uptake is less likely to have a correlation with GLUT-1 expression, hence limiting the role of FDG-PET in RCC. 1 2