Prognostic implication of extrarenal metabolic tumor burden in advanced renal cell carcinoma treated with targeted therapy after nephrectomy

Objective: In the era of targeted therapy for advanced renal cell carcinoma (RCC), appropriate prognosis prediction is necessary for optimal therapy with or without cytoreductive surgery. We evaluated prognostic implication of extrarenal metabolic tumor burden in nephrectomized patients with advanced RCC. Methods: Forty-four patients with advanced RCC who underwent ¹⁸F-fluorodeoxyglucose PET/CT were retrospectively enrolled. The patients were treated with nephrectomy and targeted therapy. On PET/CT image of each patient, maximal standardized uptake value (SUV_max) of lesions were measured, and metabolic tumor burden was measured as total lesion glycolysis (TLG) by multiplying tumor volume and mean SUV. An overall TLG was calculated as the sum of those of all lesions. The prognostic value of PET parameters (SUV_max and TLG), and established major clinical factors (serum hemoglobin and corrected calcium, and number of metastatic sites) were tested with regard to overall survival. Results: Among 44 patients, 8 died during mean follow-up time of 21.9 ± 17.7 months. On FDG PET/CT, a total of 250 lesions were analyzed. In univariate analyses, SUV_max, TLG, number of metastatic sites, serum hemoglobin and corrected calcium were significant prognostic factors. Among them, TLG remained as an independent prognostic factor in a multivariate analysis (P = 0.038). In subgroup analyses, TLG was still a significant prognostic factor in patients treated with sunitinib only and in patients on the first staging as well as restaging. Conclusions: Extrarenal metabolic tumor burden is a significant prognostic factor in advanced RCC patients treated with targeted therapy. In selection of candidates for cytoreductive surgery, the measurement of metabolic tumor burden may be effective.