Tumor ecosystem and microbiome features associated with efficacy and resistance to avelumab plus chemoradiotherapy in head and neck cancer.

Immune checkpoint blockade-based multimodal therapy is widely used across oncology; yet drivers of resistance in most cancer types are not well understood. Here, we comprehensively characterized the tumor genome, microenvironment and microbiome in a phase 3 international randomized trial ( NCT02952586 ) to identify factors that shape outcomes to anti-PD-L1 avelumab plus standard-of-care chemoradiotherapy versus placebo/chemoradiotherapy in individuals with locally advanced head and neck cancer. Patients receiving avelumab whose tumors contained distinct immunologic and genetic features had superior outcomes compared to those receiving placebo. By contrast, patients with increased myeloid/neutrophil activities had worse outcomes with avelumab than those treated with placebo. Strikingly, these tumors possessed telltale intratumoral bacteria, elevated tumor-associated neutrophils, high systemic neutrophil-to-lymphocyte ratios and suppressed adaptive immunity. We define tumor ecosystems associated with benefit to chemoimmunotherapy. Our data demonstrate how intratumoral bacteria affect immune checkpoint blockade response within a randomized trial. These discoveries enhance our understanding of combination immunotherapy, provide a useful multiomic resource and identify unanticipated interactions that may guide future therapeutic strategies.