PTEN and cancer: In addition to mutations and amplification of EGFR, abnormal activation of RAS/RAF/MEK/ERK pathway frequently occurs in cancer due to mutations in other membrane receptors, downstream effectors such as KRAS and BRAF or alternative pathways that regulate RAF activity such as phosphoinositide 3-kinase (PI3K), phosphatase and tensin homolog (PTEN) and protein kinase B (AKT) [46].