Impact of SARS-CoV-2 mRNA-BNT162b2 vaccination on survival outcomes in metastatic colorectal cancer patients treated with bevacizumab-based therapy.

3574 Background: Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide. Bevacizumab, an anti-vascular endothelial growth factor (VEGF) antibody, is widely used in metastatic CRC (mCRC) treatment to inhibit tumor angiogenesis and modulate the immunosuppressive tumor microenvironment. Recent evidence suggests that mRNA-based COVID-19 vaccines, such as SARS-CoV-2 mRNA-BNT162b2, may enhance anti-tumor immune responses. This study aimed to evaluate the impact of SARS-CoV-2 mRNA-BNT162b2 vaccination on progression-free survival (PFS) and overall survival (OS) in mCRC patients treated with bevacizumab-based therapy. Methods: This retrospective, single-center study included 92 mCRC patients treated with bevacizumab between June 2021 and October 2024. Patients were divided into vaccinated (n=50) and unvaccinated (n=42) groups. Baseline demographic, clinical, and pathological characteristics were collected. PFS and OS were analyzed using Kaplan-Meier estimates and Cox proportional hazards regression models to identify independent predictors of survival. Results: The vaccinated group demonstrated significantly longer median PFS (8.0 months vs. 5.6 months, p=0.010) and OS (39.4 months vs. 17.8 months, p=0.014) compared to the unvaccinated group. Multivariate analysis identified SARS-CoV-2 mRNA-BNT162b2 vaccination as an independent predictor of improved PFS (HR 0.44, p=0.003) and OS (HR 0.39, p=0.018). Vaccinated patients also had a higher proportion of favorable ECOG PS and a lower prevalence of RAS mutations. Conclusions: SARS-CoV-2 mRNA-BNT162b2 vaccination was associated with improved PFS and OS in mCRC patients receiving bevacizumab-based therapy, potentially through enhanced anti-tumor immune responses. These findings highlight the potential of mRNA-based vaccines to modulate the tumor microenvironment and improve outcomes in mCRC. Further prospective studies are needed to confirm these results and explore underlying mechanisms.