PIK3CA and head and neck squamous cell carcinoma: This study showed that the pan-PI3K inhibitor buparlisib was insufficient for the treatment of patients with R/M SCCHN, even though PI3K pathway alterations are frequently caused by mutations associated with SCCHN.7,8 We conducted a mouse–human co-clinical trial, with PDX models derived from biopsied tumour samples of the patients enrolled in this Phase 2 clinical trial.