Evaluation of the correlation between antibiotic use and survival in patients with recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) treated with immune checkpoint inhibitors (ICIs).
6509 Background: Recent evidence suggests that treatment with systemic antibiotics (Abx) disrupts the intestinal microbiome and may be associated with decreased survival for patients receiving treatment with ICIs for advanced cancers, including R/M HNSCC. However, a potential confounder is that Abx use identifies a subgroup of patients with a worse prognosis. The FDA examined the association between Abx use and survival for ICIs and other drugs used for the treatment of patients with R/M HNSCC. Methods: Data submitted to the FDA from three randomized controlled trials with ICI as a single agent or with chemotherapy (ICI group) compared to chemotherapy and/or cetuximab (Control group) were pooled. The association between systemic Abx use within 30 days of initiating anticancer therapy and survival for the ICI and Control groups was evaluated using Kaplan-Meier (KM) estimates and compared using Cox proportional hazards regression models, controlling for ECOG performance status, line of therapy, HPV status, PD-L1 expression, and other important prognostic factors. Results: In the ICI and Control groups, 36% and 46% of patients received Abx, respectively. For the ICI group, the difference in KM-estimated median overall survival (OS) was 5.6 months based on receipt of Abx (hazard ratio [HR] 1.70). Abx had no impact on OS for the Control group. Similar trends were observed for progression-free survival (PFS). Conclusions: In this exploratory analysis, systemic Abx within 30 days of initiating treatment for R/M HNSCC was associated with decreased survival for patients treated with ICIs compared with patients who did not receive Abx. Use of Abx had no apparent difference in survival in the control group. Further examination of the association between Abx use and clinical outcomes for patients with R/M HNSCC treated with ICIs is needed. [Table: see text]