642P - Frequent BRAF, GNAS and SMAD4 mutations identified in colorectal mucinous carcinomas

Abstract

BackgroundColorectal mucinous carcinoma (MAC) is a distinct subtype of colorectal carcinoma (CRC) accounting for approximately 10-20% of all CRCs. Mucinous carcinomas characterized by the presence of abundant extracellular mucin which occupies at least 50% of the tumour volume. Patients are often diagnosed at an advanced stage in young patients showing a poor prognosis with the 3-year overall survival rate of 57%. Although clinicopathologic findings of colorectal MACs are relatively well known, their molecular alterations have not elucidated. We investigate molecular alterations of colorectal MACs revealed by next-generation sequencing (NGS). MethodsWe retrospectively reviewed cases of CRCs with mucinous component and 111 MACs subject to molecular profiling using NGS on the Ion Proton (Thermo Fisher Scientific). We examined substitutions and small indels in 409 cancer-related genes using Ion ampliseq Cancer Hotspot and Ion ampliseq Comprehensive Cancer panels. ResultsOf the 111 patients included in the analysis, 60 (54.1%) were male: the median age was 58 years. BRAF was mutated in 17% of colorectal MACs (19 of 111) and 9.0% of CRCs (18 of 200), V600E mutations were predominantly identified in MACs, representing 95% (18 of 19) of BRAF mutated cases (p=0.0438). GNAS mutations were frequently detected in 14.4% of colorectal MACs (19 of 111) and 1.5% of CRC (3 of 200), R201C and R201H were more commonly mutated, representing 95% (18 of 19) of GNAS mutated cases (p<0.001). SMAD4 mutations were frequently noted in colorectal MACs compared with those of CRCs (24 of 111 vs. 22 of 200, p=0.0187). ConclusionsThis study demonstrates distinct genomic differences in colorectal MACs compare with CRCs. The genomic profiling of colorectal MACs revealed by NGS can identify potentially targetable molecular alterations in the majority of colorectal MACs (95.5%). Overall, colorectal MACs harbor relatively high frequencies of BRAF, GNAS, and SMAD4 mutations compared with those of CRCs. This distinct activating or inactivating mutations of these genes suggest promising consideration of targeted therapy by inhibiting related pathways in patients with advanced colorectal MACs. Legal entity responsible for the studySun Mi Lee. FundingJeju National University Hospital. DisclosureThe author has declared no conflicts of interest.