PTEN and head and neck cancer: PTEN has been shown to be lost or inactivated by multiple mechanisms in a wide spectrum of human cancer types: a loss of heterozygosity of PTEN was found in 60–80% of patients with glioblastoma and in 45% of endometrioid carcinoma of the ovary; a loss of PTEN protein expression was found in 20–40% of patients with colorectal cancer; and a decreased PTEN expression was found in 30% of patients with head and neck cancer, PTEN mutations were found in up to 40% of patients with glioblastoma and in 15–50% of patients with prostate cancer [134].