Improved survival without increased toxicity with influenza vaccination in cancer patients treated with checkpoint inhibitors.

In international guidelines, influenza vaccination is recommended to cancer patients receiving antitumor treatment. Whether this recommendation should include patients treated with the recently introduced and now widely used checkpoint inhibitors (CPIs) is unclear. The immune hyperactivation after vaccination in a patient on CPI treatment may strengthen the antitumor immunity and improve patients´ prognosis. On the other hand, the hyperactivation might increase the risk for immune-related adverse events (IRAEs). Furthermore, there is a risk for decreased antitumor effect by the phenomenon of antigenic competition. Only results from few studies addressing survival have been reported and the results from studies on IRAEs are contradictory. We performed a multi-center retrospective cohort study at three Swedish centers in patients with metastatic cancer. All patients previously not treated with CPIs and who received monotherapy with a PD-1 or PD-L1 blocker between January 1st, 2016 until May 31st, 2019 were included. The most common type of malignancy was melanoma (47.8%) followed by non-small cell lung cancer (31.0%). Statistically significant longer PFS and OS were observed in multivariate analyses at 6-month landmark time in the vaccinated compared to the non-vaccinated group after adjustment for age, gender, comorbidity, performance status, CNS metastasis and line of treatment (p = .041 and 0.028, respectively). Furthermore, the incidence of any IRAE grade was comparable between vaccinated and non-vaccinated group (p = .85). In conclusion, the current study indicates that survival improves with influenza vaccination while not increasing the risk for side effects in cancer patients treated with checkpoint inhibitors. Hence, our results strongly support influenza vaccination in cancer patients receiving checkpoint inhibitors.