Sarcopenia defined by skeletal muscle mass index at the third lumbar vertebra is a prognostic factor for extensive-stage small cell lung cancer patients: a retrospective study

Background: Small cell lung cancer (SCLC) is one of the most aggressive types of lung cancer and reliable indicators are needed for improved patient management. The evaluation of skeletal muscle index of the third lumbar vertebra (L3MI) based on computed tomography (CT) is used to estimate patient prognosis in multiple cancers. However, its function in extensive-stage SCLC remains controversial. Considering that the maintenance of muscle mass may affect the survival of cancer patients. Herein, a retrospective study was conducted to investigate whether sarcopenia defined by skeletal muscle mass index at the third lumbar vertebra is a prognostic factor in extensive-stage SCLC cancer patients.Methods: This retrospective analysis included extensive-stage SCLC patients diagnosed at the Sun Yat-sen University Cancer Center from January 2009 to March 2017 with platinum-based chemotherapy. Clinical data were collated for further examination, and CT or positron emission tomography (PET)/CT datasets were analyzed for body mass index (BMI) and L3MI. Follow-up data were collected by contacting patients or their families. Overall survival (OS) was defined as the interval between the date of treatment started and the date of death or censoring. The Kaplan-Meier product limit method and log-rank tests were used to assess differences in OS between the high L3MI and low L3MI groups. Cox regression analysis was used to identify independent factors of OS.Results: For the 139 extensive-stage SCLC patients, the median follow-up time was 26.1 months (range, 0.4 to 79.4 months). The median OS was 9.5 months. There were no differences in age, inflammatory factors, nor progression after first-line treatment between the high L3MI and low L3MI groups. Kaplan-Meier analysis showed that the OS of the high L3MI group was significantly longer than that of the low L3MI group (14.045 vs. 9.985 months; P=0.007), and multivariate analysis identified high L3MI to be an independent prognostic factor for predicting longer OS in extensive-stage SCLC patients [hazard ratio (HR), 0.623; 95% confidence interval (CI), 0.405-0.960; P=0.032].Conclusions: Sarcopenia defined by L3MI is a prognostic factor for extensive-stage SCLC patients and early intervention of muscle mass maintaining may achieve better cancer management.