Impact of flu vaccine on survival after immunotherapy for metastatic castration resistant prostate cancer (mCRPC): Analysis of Medicare claims data

e17591 Background: Sipuleucel-T (sip-T) is a cellular immunotherapy that activates a patient’s own immune system to target prostate cancer cells. Flu vaccine contains inactivated virus that stimulates the immune system to induce a response. Hypothetically, influenza vaccines may impact sip-T effectiveness by affecting the apheresis procedure, ex vivo production of sip-T, and/or CD 54+ upregulation. We explored the effect of receiving the flu vaccine on outcomes in men who received first line treatment with sip-T. Methods: Claims data from the 2013-2017 CMS Fee for Service 100% Medicare Identifiable Database for Parts A, B and D Data were examined. Among men with dates of first sip-T doses in 2014 and 2015 (ie, index dates), we identified whether or not they received flu vaccine 30 days before or after based on healthcare common procedure coding system (HCPCS) codes and National Drug Codes (NDCs). Kaplan-Meier methodology was used to assess survival with Cox proportional hazards regression model used to calculate hazard ratios (HR). Three years of follow-up (F/U) were available for men with 2014 index dates; 2 years were available for men with 2014 and 2015 index dates. Results: Approximately 8% of men received the flu vaccine (102 of 1279 with 2 years of F/U; 50 of 656 with 3 years of F/U). Overall, mean age was 76 years. Most ( > 86%) were white. Receipt of flu vaccine did not impact the overall survival of men who received sip-T (HR [95% CI], 0.93 [0.64, 1.35] at 2 years and 0.90 [0.60, 1.37] at 3 years). The resultant Kaplan-Meier curves overlapped (not shown). Conclusions: Based on these claims analyses, concomitant use of flu vaccine did not appear to impact survival outcomes after sip-T administration in men with mCRPC. These data have practical application for clinicians and patients given limited prospective data evaluating the role of flu vaccination in patients receiving immunotherapy. [Table: see text]