MTOR and head and neck squamous cell carcinoma: The HPV proteins E6 and E7 not only inhibit the P53 and Retinoblastoma tumour suppressor genes, but they can also increase the PI3K/Akt/Mammalian target of rapamycin (mTOR) signaling pathway, which is upregulated in over 90% of HNSCC, irrespective of HPV status; this increase stimulates carcinogenesis and can lead to treatment resistance [53].