P3.09-007 Thoracic Asymmetry and Its Impact on Survival after Radiation and Surgery for Malignant Pleural Mesothelioma

Staging for malignant pleural mesothelioma (MPM) remains a challenge due to poor prognostic utility. Other clinical factors may improve and refine the staging system. We investigate the impact thoracic asymmetry at time of initial presentation prior to therapy on survival in MPM patients treated with multimodal therapy. We reviewed 93 consecutive treatment naïve MPM patients treated with Surgery for Mesothelioma after Radiation Therapy (SMART protocol) from Sep 2008 to Jul 2015. The right and left axial thoracic areas (defined as the product of the ant-post and med-lat extent of hemithoraces at the level of carina) were used to calculate the asymmetric thoracic ratio (ATR, where 1 is more symmetric, Fig 1). Significant factors were determined using univariate (log rank), multivariate (Cox proportional hazards) as well as recursive partition analysis (RPA). Continuous variables were discretized into binary categories split by its median value. After a median follow-up of 15.6 months, 63 (68%) patients recurred, 56 (60%) died. The median ATR was 0.85, ranging from 0.52 to 1.00. On univariate analysis, histology (p=0.003 and 0.0002), gross tumor volume (GTV, p=0.004 and 0.001), and ATR (p=0.00001 and 0.0000002) all significantly impacted both overall and disease free survival, respectively, while mediastinal nodal involvement (p=0.03) was significantly associated with DFS only. On multivariate analysis, histology (p=0.01 and 0.005) and GTV (p=0.02 and 0.016) significantly impacted both overall and disease free survival, respectively. ATR significantly impacted disease free survival (p=0.02, HR=0.06 95% CI 0.02-0.20) and was suggestive of a trend for overall survival (p=0.07). On RPA, ATR<0.848 was significantly (p<0.001) associated with poorer DFS. A low asymmetric ratio (ATR<0.848) is significantly associated with poorer outcomes, specifically disease free survival, and is independent of histology and tumor volume. Further study is needed to validate this parameter.