Treatment of the NT8e, CAL27, AW13516 and DOK HNSCC cell lines with gamma secretase inhibitor (GSI-XXI) that abolished the presence of activated NOTCH1 (Supplementary Figure S4D) that resulted in significant reduction in soft agar colony formation (Figure 2E) and cell survival (Supplementary Figure S4E) as compared to vehicle treated in NT8e and CAL27 cells but not AW13516 cells. Here, NOTCH1 is linked to head and neck squamous cell carcinoma.