Molecular characteristics and prognostic impact of <i>GNAS</i> mutations in colorectal cancer: An international collaborative study between United States and Japan.

48 Background: GNAS (Guanine nucleotide-binding protein, alpha stimulating) encodes the alpha subunit of the stimulatory G protein, and gain of function mutations in this gene have been previously identified, especially those located at the R201 codon. Although GNAS R201C/H has been associated with mucinous histology and poor response to chemotherapy in appendiceal cancer, the impact of GNAS mutations in colorectal cancer (CRC) remains unclear. Methods: We conducted a comparative, integrative analysis of GNAS mutations in CRC using two cohorts: MD Anderson Cancer Center (MDA) across all stages (N=5,249) and the GALAXY study involving only resectable disease (UMIN000039205, N=2,599). We assessed the correlation between GNAS pathogenic mutations and microsatellite stability, CRC sidedness, co-mutations, and survival outcomes. The Chi-squared test was used for categorical variables, and the log-rank test for overall survival (OS) and disease-free survival (DFS). Results: In the MDA and GALAXY cohorts, GNAS mutations were identified in 107 (2.0%) and 61 (2.4%) patients, respectively. Prevalence of GNAS mutations was higher in right sided tumors (MDA: 3.8% vs. 1.3%, GALAXY: 6.2% vs 2.8%, p&lt;0.01 for both cohorts) and microsatellite instability-high (MSI-H) tumors (MDA: 6.5% vs. 1.8%, GALAXY: 16.5% vs. 1.4%, p&lt;0.01 for both cohorts). There was not an association of GNAS mutations with stage in either cohort. GNAS was significantly enriched for co-mutation with KRAS in the MDA cohort (OR=3.26, P&lt;0.01), similar to prior observations in appendix cancer, but was not significantly associated with KRAS mutations in the GALAXY cohort (OR=1.35, P=0.3). GNAS mutations were mutually exclusive with TP53 in both cohorts (MDA: OR=0.58, P=0.026; GALAXY: OR=0.21, P&lt;0.01). With regards to survival, in the MDA cohort, GNAS mutant tumors had a trend towards worse OS in the overall population (20 mo vs. 33 mo, HR=1.27, 95% CI=0.61-1, P=0.085). The survival impact of GNAS mutations was greatest in metastatic patients (Stage IV: 19 mo vs. 38 mo, HR=1.49, 95% CI=0.47-0.94, P=0.021 vs. Stage I-III: HR=1.35, 95% CI=0.46-1.2, P=0.22). The GALAXY cohort showed no significant association between GNAS mutations and DFS (HR=1.05, 95% CI=0.6-1.8, P=0.9). In both cohorts, GNAS mutations had a worse prognosis in left-sided CRC (MDA: HR for OS = 1.45, P = 0.091; GALAXY: HR for DFS=2.15, P=0.09) with no significant effect observed in right-sided CRC (MDA: HR for OS=0.91, P=0.68; GALAXY: HR for DFS=0.65, P=0.3). Conclusions: Our findings highlighted the intricate role of GNAS mutations in CRC, demonstrating its higher prevalence in MSI-H and right-sided colon, significant association with KRAS mutations, and divergent prognostic impacts based on tumor sidedness. Further research is needed to elucidate the mechanisms behind the worsened survival in left-sided GNAS- mutated CRC.