Malignant peritoneal mesothelioma: Clinicopathological features, prognostic factors, and survival outcomes

650 Background: Peritoneal mesothelioma (PeM) is an orphan disease with approximately 300-400 cases diagnosed in the United States each year. Due to its rarity, data on its presentation and prognostic factors is limited. The purpose of this study was to investigate the clinicopathological profile and outcome of Malignant PeM (MPeM). Methods: We retrospectively reviewed 128 PeM patients (pts) seen at UTMDACC (2011 - 2017) comprised of 111 MPeM and 17 variants (VPeM) [9 well-differentiated papillary and 8 multicystic]. Kaplan-Meier method was used to estimate median overall survival (mOS) and compared with log-rank tests. Results: Median age at diagnosis was 57 yrs. with a higher proportion of women (61%). The mOS for MPeM was significantly shorter than VPeM (HR 3.7, 95% CI: 1.6 – 8.4, P = 0.002). Among pts with MPeM, median age at diagnosis was 56 yrs. and 58% were women. Only 22% had prior exposure to asbestos. Epithelioid subtype was seen in 94 (85%) pts. Calretinin and WT-1 IHC were positive in 98% and 96% of cases. BerEP4 and MOC-31 IHC were negative in 90% and 84% of cases. After median follow-up of 31 months (m), the mOS for MPeM cohort was 78 m. In univariate analysis, age, prior asbestos exposure, ECOG PS, histologic subtype, CA125, neutrophil-lymphocyte ratio (NLR) and cytoreductive surgery (CRS) were found to be associated with OS. In multivariate analyses, age ≥ 65 years (HR 4.5, 95% CI: 1.3 - 15.2, P = 0.02), prior asbestos exposure (HR 4.1, 95% CI: 1.1 – 15.6, P = 0.04), poor PS (ECOG 2/3) (HR 8.9, 95% CI: 1.7 – 47.7, P = 0.01), elevated CA125 ( > 3X upper limit of normal) (HR 4.5, 95% CI: 1.3 – 15.5, P = 0.02), and high NLR (HR 3.8, 95% CI: 1.1 – 12.6, P = 0.03) were found to be independently associated with poor OS. A total of 50 (45%) pts underwent CRS and among these the completion of cytoreduction score (CCS) was strongly associated with OS (mOS: 201 m, 53 m and 36 m for CCS 0, 1, 2/3, respectively, P = 0.005). Conclusions: MPeM is associated with poor survival outcomes. Prognostic factors include age, history of asbestos exposure, CA-125 level, NLR, and PS. CRS with CCS 0 results in favorable survival. Further understanding of molecular genetics is warranted to improve prognostication and outcomes.