Antibiotics use decreases survival in cutaneous squamous cell carcinoma patients receiving immune checkpoint inhibitors

Immune checkpoint inhibitors (ICI) have become the first-line therapy in patients with advanced cutaneous squamous cell carcinoma (cSCC). Antibiotics (ATB) have been reported to reduce ICI response in cancers, but this has not been evaluated in cSCC.

To evaluate ATB exposure at the onset of ICI in cSCC patients and to analyze its impact on outcome.

This single-center retrospective study included all patients who started anti-PD-1 for cSCC between March 2019 and July 2023. Exposure to ATB within 3 months prior and after the onset of ICI (ATB 3-3), including patients exposed within 1 month prior and after (ATB 1-1) were recorded. Response to ICI and survival were compared between patients with or without ATB exposure.

Among 104 patients included, 45 % were classified into ATB 3-3 subgroup, and 20 % to ATB 1-1. Disease control rate at 3 months were lower in both ATB 1-1 and ATB 3-3 subgroups, compared to their control group (p = 0.02 and 0.03, respectively). The overall survival and disease specific survival were lower in the ATB 1-1 subgroup, compared to control group (p = 0.04 and p = 0.01, respectively). Median progression free survival was 127 days in ATB 1-1 group, significantly lower than the control group (not reached), p = 0.005.

ATB intake was very frequent at ICI initiation in cSCC patients. In our cohort, ATB use within 1 month before or after ICI initiation significantly impacted survival, highlighting the need for caution when prescribing antibiotics in this population.