Session Item

Pre- and peritherapeutic antibiotics administration has been shown to negatively impact the oncological outcome of melanoma and lung cancer patients receiving immune checkpoint inhibitors, possibly by affecting the microbiome-immune system-cancer axis. We therefore aimed to explore the effects of antibiotic application on the outcomes of head-and-neck squamous cell carcinoma (HNSCC) patients undergoing definitive (chemo)radiotherapy [(C)RT].

In this single-center retrospective study, a cohort of 220 HNSCC patients who were treated with (C)RT between 2010 and 2019 was evaluated. Information about antibiotics application including indication, duration and drug classes were collected from electronic patient records. Patient and treatment characteristics were compared depending on antibiotic usage with t-tests and chi-square tests. The influence of antibiotics administration on progression-free (PFS) and overall survival (OS) was determined with Kaplan-Meier analyses.

A total of 154 patients (70%) received antibiotics in a time interval ranging between 30 days before (C)RT until treatment completion. ECOG status, age, N stage, radiotherapy dose and radiotherapy completion rate showed no differences between patients with and without antibiotics treatment, whereas patients who received antibiotics exhibited higher T stages and more often underwent RT instead of CRT. While 93 patients (42%) obtained antibiotics during the 30 days prior to (C)RT initiation, 100 (46%) were treated with antibiotics during (C)RT. The most frequent indication of antibiotics prescription was single-shot antibiotic prophylaxis before port catheter implantation (n=132). Peritherapeutic antibiotics administration significantly worsened both PFS (median 10 vs. 24 months, p<0.05) and OS (median 26 vs. 36 months, p<0.05), while pretherapeutic usage had no effect. This effect was found pronounced in the cohort of patients aged <75 years (median PFS 10 vs. 44 months, p<0.05, and median OS 26 vs. 54 months, p<0.05), whereas there was no significant difference among older patients (≥75 years).

Peri- but not pretherapeutic antibiotic usage was associated with reduced PFS and OS in HNSCC patients receiving (C)RT. In the future, microbiome analyses may help to better understand the mechanisms underlying the observed effects of antibiotic use in HNSCC patients receiving (C)RT.