Clinical outcome, treatment modalities and overall survival in microsatellite stable and unstable colon cancers: A National Cancer Database (NCDB) analysis.

e15702 Background: Colon cancers (CC) can be classified as microsatellite stable (MSS) and microsatellite instability-high (MSI-H) cancers. This study aims to compare clinical outcomes, treatment modalities, and overall survival across these cohorts. Methods: MSS and MSI-H CC from 2010 to 2020 were identified using the National Cancer Database (NCDB). Baseline characteristics were described for the cohorts. Fisher’s exact test was used to compare categorical variables, and the Mann–Whitney U test was used for continuous variables. The 3-year and 5-year survival rates were estimated using the Kaplan-Meier method with the log-rank test. Additionally, the Cox proportional hazard model was employed to compare overall survival and evaluate prognostic factors. Results: We identified a total of 102,834 patients, with 91.3% having MSS CC, while 8.7% having MSI-H CC. The median ages for patients with MSS and MSI-H CC were 66 and 69 years, respectively. Females were more likely to have MSI-H (57.5%) compared to MSS (48.5%) (p < 0.001). The most common stage at diagnosis was Stage II for MSS (43.4%) and Stage III for MSI-H (32%). Patients with MSI-H received lower rates of chemotherapy (CT) (32% vs. 44%) and immunotherapy (3% vs. 5%) compared to those with MSS CC. Overall survival was higher for MSI-H CC, with a median overall survival (mOS) of 55.8 months versus 51.3 months (MSS) on both univariate analysis (p < 0.001) and multivariate analysis (hazard ratio [HR]: 0.87; 95% CI: 0.84–0.91; p < 0.001). Also, MSI-H patients were noted to have better survival in Stages I–II but worse in Stages III and IV. On further analysis of Stage IV CC, 78% of those with MSS received chemotherapy, versus 69% with MSI-H CC. Additionally, 26.8% of MSS CC and 25.8% of MSI-H CC patients received immunotherapy. There was no difference in survival among Stage IV CC patients with MSS and MSI-H CC on both univariate analysis (3-year OS: 35.1% vs. 35.4%; p = 0.9) and multivariate analysis (HR: 0.92; 95% CI: 0.84–1.00; p = 0.058). Among patients with Stage IV MSI-H CC, there was a significant benefit of chemotherapy (3-year OS: 45.6% vs. 18.3%; p < 0.001; HR: 0.51; 95% CI: 0.42–0.62; p < 0.001) and immunotherapy (3-year OS: 46.6% vs. 31.5%; p < 0.001; HR: 0.67; 95% CI: 0.54–0.82; p < 0.001). Of the patients with MSI-H CC, there was no significant difference in survival between groups receiving chemotherapy (383) and chemoimmunotherapy (186) on both univariate analysis (3-year OS: 41.2% vs. 45.2%; p = 0.07) and multivariate analysis (HR: 0.87; 95% CI: 0.69–1.1; p = 0.25). Conclusions: Patients with MSI-H CC tend to have better survival at earlier stages compared to later stages. Also, there was no difference in survival with chemo-immunotherapy versus chemotherapy in Stage IV MSI-H CC. However, with the advent of immunotherapy using PD-L1 agents, the treatment paradigm is starting to change, warranting further studies.