Molecular profiling of appendix-derived pseudomyxoma peritonei (PMP).

Abstract

571 Background: PMP is a rare malignancy originating from the appendix, characterized by disseminated mucinous tumor implants on peritoneal surfaces. Cytoreductive surgery and intraperitoneal chemotherapy offers optimal outcomes for most patients; however, for patients that progress, there are few treatment options. We examined the role of multiplatform molecular profiling to study biomarker-guided treatment strategies for this rare malignancy. Methods: 54 patients with appendix-derived PMP were included in the study and tested centrally at Caris Life Sciences (Phoenix, AZ). Tests included one or more of the following: gene sequencing (Sanger or next generation sequencing [NGS]), protein expression (immunohistochemistry [IHC]) and gene amplification (C/FISH). Results: Targeted sequencing of 47 genes detected variants in KRAS (79%), GNAS (73%) and SMAD4 (18%). Mutations were found at low frequencies (n = 1-2) in APC, ATM, BRAF, PIK3CA, MLH1 and TP53. GNAS and KRAS co-occurrence was found in 38%. High rates of protein overexpression were found in EGFR (83%), cMET (59%), cKIT (58%) and PDGFRA (58%), respectively. Immune checkpoint expression was found in 36% (PD1-positive tumor infiltrating lymphocytes) and 9% (PDL1 tumor expression). Expression of surrogate markers of cell proliferation were found at low rates (TLE3 27%, TOP2A 22%), consistent with the slow-growing biology of PMP. PTEN was intact (wild type [100%] and positive IHC [80%]) in the majority of PMP. Patients exhibit stable microsatellite status and mismatch repair proficiency in 93% of patients. Importantly, multidrug resistance protein expression was found at high levels (100% BCRP, 94% MRP1, 88% PGP). Markers for gemcitabine (RRM1), fluorouracil (TS), oxaliplatin (ERCC1) and irinotecan (TOPO1) chemo-sensitivities were found to be favorable in 93%, 87%, 77% and 65%, respectively. Conclusions: Molecular profiling by multiple platforms identified potential therapy options in the non-targetable setting of a KRAS-mutated population. The role of cMET-targeted therapies and immune checkpoint inhibitors merit further investigation. Biomarker-guided selection of cytotoxic chemotherapies may facilitate responses to systemic treatment.