Somatic mutation landscape of appendiceal cancer.

Abstract

671 Background: Appendiceal cancers are rare, comprising just 0.5% of all intestinal neoplasia, which has prevented the systematic study of these tumors in randomized clinical trials. Given this absence of clinical data, no evidence-based guidelines exist regarding the best management of this disease. Standard treatment generally follows consensus guidelines for colorectal cancer; however, there are currently no standards to guide chemotherapy selection in the adjuvant or metastatic setting. Methods: Somatic mutation profiles covering ~300 frequently mutated genes were obtained for 385 primary appendiceal tumors (Foundation Medicine). A retrospective review was performed to gather clinico-pathologic data. The primary objective was to assess the somatic mutation profile of each subtype of appendiceal cancer and to compare these to colorectal cancer. Colorectal data was obtained from TCGA cohort via cBioPortal. Results: Appendiceal adenocarcinoma (non-mucinous) and mucinous adenocarcinoma had shared somatic mutations albeit with differing frequencies. The most common mutations were KRAS (60.1% and 80.5%, respectively), GNAS (32.4%, 58.5%), TP53 (42.8%, 19.5%), and SMAD4 (14.8%, 14.6%). Tumors with goblet cell (adenocarcinoid) histology had lower prevalence of KRAS (16.0%) and GNAS mutations (8.0%), but similar prevalence of TP53 mutation (24.0%) and a greater prevalence of ARID1A mutation (20.0%). The mutation profiles of all appendiceal histologies differed from colorectal adenocarcinoma with markedly lower prevalence of ATM (7.9% vs. 71.0%). Chemotherapy data was available for 30 metastatic patients; these patients received an average of 1.76 lines of therapy (range 1-4). All 30 were treated with either 5-FU or capecitabine, 11 (36.7%) with oxaliplatin, 23 (76.7%) with irinotecan and 19 (63.3%) with bevacizumab. Analysis of survival data and correlation with molecular and histologic features is ongoing. Conclusions: Despite clear molecular differences between appendiceal and colorectal tumors, appendiceal tumors are primarily treated with colorectal chemotherapy regimens. There remains a pressing need for both pre-clinical and clinical investigation to develop treatment regimens specific to appendix cancer.