Our findings suggest that NOTCH1MUT predicts response to PI3K/mTOR inhibitors, which may lead to the first biomarker-driven targeted therapy for HNSCC….E. From our panel of 59 HNSCC cell lines, we identified 24 harboring NOTCH1 and/or PIK3CA mutations....NOTCH1MUT cells overexpressing PDK1 had higher expression levels of p-AKT, p-S6, and p-4EBP1 (Fig. 5C), and they had decreased apoptosis after GSK2126458 treatment (Fig. 5D and E).