At a median follow-up of 3.1 years, median OS in the overall patient cohort was 43.7 months and 27.4 months for those with and without antibiotic exposure (log-rank P =.01). On multivariable analysis controlling for multiple confounding factors, the hazard ratio (HR) associated with antibiotic exposure was 1.95 (95% CI, 1.43-2.66; P <.001).

When similar analyses were performed separately for patients with stage III and stage IV disease, the respective HRs were 1.81 (95% CI, 1.27-2.57; P =.001) and 2.78 (95% CI 1.31-5.87; P =.007). Notably, when only the subgroup of patients with stage III disease treated with ICIs following surgery (ie, in the adjuvant setting) was considered in the analysis, the HR was 4.84 (95% CI, 1.09-21.50; P =.04), with survival favored in those not exposed to antibiotics.

Another study finding showed an increased 1-year cumulative risk of immune-related colitis requiring intravenous steroids for those exposed to antibiotics vs not exposed (9.8% vs 4.6%; P =.03), with an HR on multivariable analysis of 2.14 (95% CI, 1.02-4.52; P =.046) for this comparison.

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Regarding antibiotic class, penicillins, cephalosporins, and fluoroquinolones were all associated with survival detriments when administered to patients within 3 months of the first infusion of ICI.

“Given the known overutilization of antibiotics in current society, physicians should exercise caution when considering antibiotic prescription in cancer populations treated with ICI. These findings are particularly relevant for patients undergoing surgery for stage III or IV melanoma, in whom adjuvant ICI therapy is planned, as injudicious antibiotic use in the postoperative setting should be avoided if possible,” the study authors remarked in their conclusion.


Mohiuddin JJ, Chu B, Facciabene A, et al. Association of antibiotic exposure with survival and toxicity in patients with melanoma receiving immunotherapy [published online April 15, 2020]. J Natl Cancer Inst. doi: 10.1093/jnci/djaa057