P198 Thoracic skeletal muscle loss is prognostic in malignant pleural mesothelioma

Introduction There are little data describing the prevalence of cancer cachexia or factors associated with this syndrome, including skeletal muscle loss, in patients with malignant pleural mesothelioma (MPM). We investigated the prognostic significance of thoracic muscle loss in patients with MPM who received chemotherapy. Methods Baseline clinical information was collected regarding 113 patients in the Prediction of Resistance to Chemotherapy Using Somatic Copy Number Variation in Mesothelioma study (PRiSM) study. 107/113 patients had an identifiable fourth thoracic vertebrae (T4). Image analysis for body composition was based on a single image at T4 on pre-chemotherapy and response assessment contrast-enhanced Computer Tomography (CT) scans. Using established Hounsfield Unit thresholds, skeletal muscle groups were manually segmented using ImageJ software. Skeletal muscle mass area (cm2) at T4 was normalised for height (cm2/m2) to calculate skeletal muscle index (SMI). Skeletal muscle loss was defined as response assessment skeletal muscle index/pre-chemotherapy skeletal muscle index ratio Results 65/113 eligible patients were included, based on available T4 imaging and height measurements. 23/65 (35%) patients lost skeletal muscle between pre-chemotherapy and response assessment CT scans. In a multivariate model, T4 skeletal muscle loss was a significant and independent predictor of shorter OS (HR 3.54 (CI 1.04–12.05), p=0.043). The median OS was 361 days (CI 271–384) in those losing skeletal muscle and 553 (CI 410–607) days in those not (p=0.007, figure 1). There were weakly negative correlations between response assessment SMI and response assessment white cell count (rs=–0.287), response assessment neutrophils (rs=–0.326) and response assessment neutrophil lymphocyte ratio (rs=–0.297). Conclusion Thoracic skeletal muscle loss is prognostically significant in patients with MPM who received chemotherapy. Skeletal muscle loss appears to be linked with neutrophil-associated inflammation, but a larger study is needed.