The catalytic subunit (p110a) of phosphatidylinositol-3-kinase (PI3K) is encoded by the PIK3CA gene and acts to activate several signaling cascades, including the well-characterized AKT-mTOR pathway that promotes cell survival, proliferation, growth and motility. PIK3CA is among the most commonly mutated genes in cancer and aberrant activation of PI3K is a transforming event. Somatic mutations in PIK3CA have been found in 1--3% of NSCLC and genetic alteration in PIK3CA have been identified in 7% of lung adenocarcinomas. These mutations typically occur within specific hotspot regions. PIK3CA mutations activate the PI3K-PTEN-AKT pathway which is downstream from both the EGFR and the RAS-RAF-MAPK pathways. The somatic mutations found thus far in PIK3CA are oncogenic, and the majority of them are clustered within exon 9 and 20 (helical and kinase domains), with three hotspots (E542K, E545K, and H1047R/L). PIK3CA mutations have been reported in 8-21% and 20-33% of head/neck and anal squamous cell carcinoma, respectively. PIK3CA mutations, especially ones involving the helical domain, in these types of squamous cell carcinoma are highly associated with HPV. The predictive and prognostic significance of PIK3CA mutations in squamous cell carcinoma is unclear and needs further elucidation. Clinical trials targeting PI3K/Akt/mTor pathway inhibitors are available for patients with PIK3CA mutated tumors.