FAT1 and head and neck squamous cell carcinoma: To explore whether FAT1 alterations and its associated downstream molecular signaling play a role in tumorigenesis we used representative HNSCC-derived cells displaying prototypical FAT1 alterations as evidenced by exome sequencing of a large cell panel25, and identified SCC25 (FAT1 copy loss), CAL27 (heterozygous FAT1 copy loss), and CAL33 (hemizygous FAT1 K3504X mutation and loss of the remaining allele) as displaying abnormal levels of FAT1 protein compared to NOKs exhibiting wild-type FAT1 (Fig. 4a).