Background and Importance Taking antibiotics weeks before immunotherapy alters the gut microbiota. It is therefore questionable whether the use of antibiotics prior to immunotherapy is associated with decreased effectiveness in cancer patients.

Aim and Objectives To evaluate the influence of the use of antibiotic therapy on the effectiveness of immunotherapy treatment in cancer patients.

Material and Methods Observational, retrospective, 68-month, retrospective study (January 2018 to August 2023) in patients diagnosed with renal cell, non-small-cell lung and head and neck cancers.

The difference in effectiveness was measured by comparing the median progression-free survival (mPFS) and median overall survival (mOS) of patients who received antibiotic therapy 2 months prior to the start of immunotherapy and those who did not receive antibiotic therapy.

Variables age, sex, Eastern Cooperative Oncology Group (ECOG) scale, immunotherapy received, number of previous lines, antibiotic prescription 2 months prior to the start of immunotherapy and duration of treatment.

Data source computerised medical records and electronic prescribing programme.

Results A total of 138 patients (71.0% male; median age 67 years) were analysed. Of the patients, 42.0% received antibiotic therapy 2 months prior to the start of immunotherapy.

The group receiving antibiotherapy (56.8% male; median age 68 years): ECOG < 1 (89%), by immunotherapy (pembrolizumab: 58%; atezolizumab: 23%; nivolumab: 19%), number of previous lines (2[1–3] median). mPFS was 5.1 (3.2–7.1) months and mOS was 16.4 (12.7–22.5) months.

The antibiotic-naive group (81% male; median age 65 years): ECOG < 1 (91%), by immunotherapy (pembrolizumab: 54%; atezolizumab: 28%; nivolumab: 18%), number of prior lines (2[1–3] median). mPFS was 5.6 (4.6–9.5) months and mOS was 17.8 (12.6–21.8) months.

The differences in both groups on mPFS and mOS were not statistically significant (p=0.57) and (p=0.78), respectively.

Conclusion and Relevance Despite limitations in sample size, our study reveals that the use of antibiotic therapy 2-months prior to the start of immunotherapy does not make a difference to the effectiveness of immunotherapy.

References and/or Acknowledgements 1. No conflict of interest.

Conflict of Interest No conflict of interest.