NRAS and colorectal carcinoma: In a proof-of-concept study, the amplification of Erb-B2 Receptor Tyrosine Kinase 2 (ERBB2) gene, an oncogenic driver and a prognostic and predictive biomarker in CRC [92], was identified as a driver of cetuximab resistance in KRAS/NRAS/BRAF/PI3KCA wild-type metastatic CRC PDXs, and was found to predict response to Epidermal Growth Factor Receptor (EGFR) and Human Epidermal Growth Factor Receptor 2 (HER2) targeted therapies [45].