Postoperative Changes in Skeletal Muscle Mass Predict Survival of Patients With Metastatic Renal Cell Carcinoma Undergoing Cytoreductive Nephrectomy

Background Sarcopenia, or the degenerative loss of skeletal muscle mass, develops as a consequence of cancer–host interactions, including systemic inflammation and poor nutritional status, and is associated with a poor prognosis in patients with metastatic renal cell carcinoma (mRCC). We explored whether postoperative changes in skeletal muscle mass after cytoreductive nephrectomy (CN) can predict the prognosis of patients with mRCC. Patients and Methods The present retrospective study included 37 mRCC patients undergoing CN at a single cancer center. The skeletal muscle index (SMI) was calculated by measuring the skeletal muscle areas at the third lumbar vertebra level on computed tomography images taken ≤ 1 month before and 5 to 6 months after CN. The percentage of change in the SMI (ΔSMI) was calculated as [(postoperative SMI − preoperative SMI)/preoperative SMI] × 100, and the association with overall survival (OS) was analyzed. Results During the follow-up period (median, 61 months for survivors), 16 patients (43%) died for a 3-year OS rate of 63%. The ΔSMI was significantly associated with OS (hazard ratio, 0.92; P < .001). When the patients were categorized into 3 groups according to the ΔSMI (decreased, 12 patients with ΔSMI ≤ −5; stabilized, 15 patients with ΔSMI < 5; and increased, 10 patients with ΔSMI ≥ 5), the OS curves were distinctly separate, with a 3-year OS rate of 19%, 76%, and 100%, respectively (P < .001). Conclusion Postoperative changes in the SMI after CN predict OS for patients with mRCC. SMI kinetics is a novel biomarker that can serve as a useful surrogate for the prognosis of patients with mRCC undergoing CN.