Association of influenza vaccine and risk of recurrence in patients undergoing curative surgery for colorectal cancer.

BACKGROUND There is increasing evidence that the inactivated influenza vaccine contains immunostimulatory properties that favor cytotoxicity and benefit survival in large population-based studies. This study aimed to determine whether an influenza vaccine was associated with risk of recurrence, overall mortality, and disease-free survival in patients undergoing curative surgery for colorectal cancer. MATERIAL AND METHODS We performed a register-based study based in Denmark in the period 2009-2015. The primary outcome was a risk of recurrence, while the secondary outcomes were overall mortality and disease-free survival. RESULTS A total of 9869 patients were included, with 5146 patients receiving an influenza vaccine between one year before and six months after surgery. In a multivariate Cox regression model, there was no association with risk of recurrence (HR 0.94, 95% CI 0.85-1.05), overall mortality (HR 0.95, 95% CI 0.87-1.03), and disease-free survival (HR 1.01, 95% CI 0.94-1.09). In patients receiving the vaccine between six and twelve months before surgery, we found an association to decreased risk of recurrence (HR 0.78, 95% CI 0.67-0.91) but no association with overall mortality (HR 1.04, 95% CI 0.93-1.17) or disease-free survival (HR 0.97, 95% CI 0.88-1.07). Subgroup analysis of patients revealed contradictory results. CONCLUSION We believe that this study's findings support the need for further clinical studies to investigate the causal effects of the influenza vaccine on oncological outcomes.