PTEN and colorectal cancer: HER2-amplified tumors with loss of PTEN (Phosphatase And Tensin Homolog) do not respond to trastuzumab4 and EGFR-amplified non-small cell lung and colorectal cancers with mutations in KRAS (Kirsten rat sarcoma viral proto-oncogene) do not respond to EGFR-targeted agents.4