PIK3CA and head and neck squamous cell carcinoma: In the study of The Cancer Genome Atlas Network for HNSCC, the percentages (%) of PTEN genetic alterations in HPV (+) and HPV (-) tumours were 12% and 6%, respectively [34], and either PTEN mutation or inhibition could result in PIK3CA/CCND1/CDK6 pathway activation and thereby enhance cell proliferation [34].