Buparlisib and Paclitaxel in Patients with Head and Neck Squamous Cell Carcinoma: Immunogenomic Biomarkers of Efficacy from the BERIL-1 Study

Background BERIL-1 was a randomized phase 2 study that studied paclitaxel with either buparlisib, a pan-class I PIK3 inhibitor, or placebo in patients with recurrent or metastatic (R/M) head and neck squamous cell cancer (HNSCC). Considering the therapeutic paradigm shift with immune checkpoint inhibitors (ICIs) now approved in the first-line setting, we present an updated immunogenomic analysis of patients enrolled in BERIL-1, including patients with immune-infiltrated tumors. Objective The objective of this study was to identify biomarkers predictive of treatment efficacy in the context of the post-ICI therapeutic landscape. Patients and Methods Genomic analyses were performed at baseline on tumor and/or plasma circulating DNA (ctDNA) samples, and immunohistochemistry (IHC) studies, including immune infiltration [tumor-infiltrating lymphocytes (TILs) and CD8 expression], were performed on tumor samples. Immunogenomic biomarkers were correlated to overall survival (OS). Results Among 158 patients enrolled in BERIL-1, either tumor (53.2%; n = 84) or ctDNA samples (70.8%; n = 112) were available in 85.4% (n = 135). The most commonly mutated genes were TP53 (57.0%), NOTCH1 (23.7%), and PIK3CA (22.2%). In the IHC studies, 98.6% (n = 68/69) of patients were TILs positive in the buparlisib arm versus 94.4% (n = 68/72) in the placebo arm. In patients with TILs-positive tumors, enrichment for clinical benefit on the buparlisib arm was seen in those with PIK3 pathway activation [25.0% (n = 17/68)] with a hazard ratio (HR) for death of 0.43 [95% confidence interval (CI) 0.21–0.87, p = 0.016]. Similarly, improved OS was seen in patients on the buparlisib arm and NOTCH pathway activation [20.5% (n = 14/68)] with a HR for death of 0.40 (95% CI 0.18–0.90, p = 0.022). Both associations were absent in the placebo group. TP53 and tumor mutational burden (TMB) did not correlate with OS in the buparlisib or placebo arms. Conclusions In this immunogenomic analysis of BERIL-1, improved HRs for OS were seen in patients with tumor immune infiltration and selected oncogenic alterations, including PIK3 and NOTCH pathway activation (NCT01852292).