External validation of prognostic indices for overall survival of malignant pleural mesothelioma

Abstract Objective There are several prognostic indices (PIs) to predict overall survival (OS) in malignant pleural mesothelioma (MPM) patients. Before using a clinical prediction model in the actual clinical setting, empiric evaluation of its performance based on datasets that were not used to develop the model (i.e., external validation) is essential. The purpose of this study was to conduct an external validation of the PIs for MPM. Materials and methods A retrospective cohort study was performed on MPM patients treated at 2 tertiary hospitals in Japan between 2007 and 2015. The primary outcome was OS. Harrell’s c-index, and was calculated to examine the discrimination of three models. The bootstrapping technique was used to evaluate optimism. Results The participants comprised 183 patients who underwent surgical treatment (n = 61), chemotherapy (n = 101), and best supportive care (BSC, n = 21). The median OS rates were 1014 days for surgery, 690 days for chemotherapy, and 545 days for best supportive care (BSC). The respective discriminations (95% confidence interval) of the Eastern Cooperative Oncology Group Performance Status, the European Organisation for Research and Treatment of Cancer index, regimen, PS, histology or stage (rPHS) index, and Tagawa index for the OS of MPM patients were 0.532 (0.444–0.620), 0.560 (0.472–0.648), 0.584 (0.452–0.716), and 0.525 (0.453–0.596) for surgery; 0.632 (0.539-0.724), 0.622 (0.548–0.696), 0.677 (0.587–0.766), and 0.545 (0.436–0.653) for chemotherapy; and 0.504 (0.365–0.644), 0.583 (0.456-–0.710), 0.704 (0.508–0.899), and 0.583 (0.436–0.730) for BSC. Conclusions Each PI showed poor discrimination for MPM patients who underwent surgical treatment. The rPHS index showed moderate discrimination for patients given chemotherapy and BSC.