Association of antibiotic treatment with survival outcomes in treatment-na?ve melanoma patients receiving immune checkpoint blockade

Purpose: The interaction of gut microbiome and immune system is being studied with increasing interest. Disturbing factors, such as antibiotics may impact the immune system via gut and interfere with tumor response to immune checkpoint blockade (ICB). Methods: In this multicenter retrospective cohort study exclusively treatment -naive patients with cutaneous or mucosal melanoma treated with first -line anti -PD -1 based ICB for advanced, non-resectable disease between 06/ 2013 and 09/2018 were included. Progression -free (PFS), and overall survival (OS) according to antibiotic exposure (within 60 days prior to ICB and after the start of ICB vs. no antibiotic exposure) were analyzed. To account for immortal time bias, data from patients with antibiotics during ICB were analyzed separately in the time periods before and after start of antibiotics. Results: Among 578 patients with first -line anti-PD1 based ICB, 7% of patients received antibiotics within 60 days prior to ICB and 19% after starting ICB. Antibiotic exposure prior to ICB was associated with worse PFS (adjusted HR 1.75 [95% CI 1.22-2.52]) and OS (adjusted HR 1.64 [95% CI 1.04-2.58]) by multivariate analysis adjusting for potential confounders. The use of antibiotics after the start of ICB had no effect on either PFS (adjusted HR 1.19; 95% CI 0.89-1.60) or OS (adjusted HR 1.08; 95% CI 0.75-1.57). Conclusions: Antibiotic exposure within 60 days prior to ICB seems to be associated with worse PFS and OS in melanoma patients receiving first -line anti-PD1 based therapy, whereas antibiotics after the start of ICB do not appear to affect PFS or OS.