Comprehensive genomic sequencing of appendiceal cancer tumors to identify different genomic alterations by subtype, novel treatment opportunities, and improved outcomes.

Abstract

599 Background: Appendiceal cancers are rare and consist of mucinous (M), adenocarcinoma (A), goblet cell carcinoma (GCC), pseudomyxoma peritonei (PMP), and several even rarer histologies. Current treatment involves surgical resection or debulking; no standard exists for adjuvant chemotherapy or metastatic disease treatment. Systemic treatment is often based on chemotherapy regimens used in colorectal cancer. Methods: Tissue from 518 appendiceal cancer patients was assayed by hybrid-capture based comprehensive genomic profiling (CGP) in the course of clinical care to evaluate genomic alterations (GA: base substitutions, indels, amplifications, copy number alterations, fusions/rearrangements) and targeted therapy opportunities; 315 genes frequently altered in cancer were assayed. Tumor mutational burden (TMB) was calculated from a minimum of 1.11 Mb sequenced DNA and reported as mutations/Mb. Results: Profiling across all appendiceal cancer histological subtypes identified different patterns in GAs across subtypes (table), most notably in GNAS, KRAS, and TP53. No PMP exhibited microsatellite instability (MSI-H) or high TMB ( > 20 mutations/Mb); MSI-H cases included 3 M, 4 A, 1 GCC; 3-7% 12% A and 6% m had high TMB. Case reports of patients with tumors harboring GNAS alterations showed response to MEK inhibitors. Conclusions: Genomic profiles of tumors from patients with appendiceal cancers reveal differing profiles from colorectal cancers (CRC) and considerable heterogeneity between subtypes, suggesting an individualized approach to treatment. Therapeutic options include clinical trials targeting pathways involving KRAS, BRAF, GNAS, PIK3CA, FBXW7, SMAD4, APC, and ATM. Recent case reports indicate that GNAS is a clinical target for MEK inhibitors. Overall, given the poor prognosis of advanced stage appendiceal carcinoma patients, CGP may identify novel, unanticipated therapeutic targets in a significant subset of patients, including immunotherapy for high TMB patients. [Table: see text]