PIK3CD and head and neck squamous cell carcinoma: And a low frequency of HNSCC cases has mutations in AKT2 and mTOR or its regulatory subunits, RICTOR and RAPTOR. A network-based analysis of the HNSCC oncogene revealed that a high percentage of lesions also exhibit loss of at least one copy of a candidate PI3K/mTOR pathway tumor suppressor gene (TSG), PTEN (31%), TSC1 (11%), TSC2 (13%), STK11 (34%), and EIF4EBP1 (36%) [20].