Outcomes of appendiceal cancer treated at a state peritonectomy service.

3629 Background: Appendiceal cancers (AC) are rare with varied prognosis. Nomenclature refined by the WHO 2019 classification is: appendiceal mucinous neoplasms (AMNs), adenocarcinomas (AA) including mucinous (MAC), not otherwise specified (ANOS), signet ring (SRC) and goblet cell (GCA), and neuroendocrine tumours (NET). Cytoreductive surgery and heated intraperitoneal chemotherapy (CRS+HIPEC) is the definitive treatment. The role of chemotherapy remains unclear with conflicting outcomes and there is need to delineate the optimal regimen in different disease settings. The aim of this study was to evaluate AC treatment and clinical outcomes by the WHO 2019 classification and analyse the impact of perioperative chemotherapy. Methods: We reviewed prospective data from the database at an Australian state peritonectomy service, Apr 2017-Dec 2021. Variables included demographics, tumour characteristics, treatment details and survival outcomes. Analysis was by the Kaplan-Meier method using the log-rank test for statistical comparison (SPSSv27). Results: 115 patients (of 207 referred) with confirmed AC proceeded to CRS. Histopathology comprised 49 AMNs (43%), 62 (63%) AA, 3 SRCs and 1 NET. The mean age was 56y (21-78), 53% female. 94% had CRS+HIPEC (Mitomycin 85%). 70% had cytoreductive score 0. The median peritoneal cancer index was 23 (0-39). 20 (17%) had localised (M0) disease, 10 acellular mucin (M1a) and 85 (74%) metastases (M1b/c). 71% were lymph node negative (N0). 40% had chemotherapy (oxaliplatin/5-fluorouracil 57%). 8 of 15 who had molecular testing had a KRAS mutation. Median follow-up was 26m (1.9-167). The table shows univariate survival analysis. Conclusions: This is the first study evaluating outcomes of perioperative chemotherapy for AC in a cohort of patients since the WHO 2019 classification. MAC have worse survival compared to ANOS, but similar to GCAs. Peritoneal acellular mucin has a similarly improved prognosis to patients with no peritoneal disease compared to those with cellular disease. Chemotherapy demonstrated worse survival compared to no chemotherapy, also seen in the literature and likely influenced by selection of more aggressive disease. There is a need to develop biomarkers and better treatments to improve the survival of these patients. Further multivariate analysis for prognostic and predictive factors is planned.[Table: see text]