NOTCH1 and head and neck squamous cell carcinoma: Additionally, the NOTCH1 tumor suppressor role is also underlined by the loss or inactivating mutations of members of the NOTCH signaling pathway in human cancers, particularly in head and neck squamous cell carcinoma (HNSCC), in which inactivating mutations of NOTCH1 were found in 10–15% of the tumors (5, –, 10).