ERBB2 and breast cancer: In a study by Prat et al., where microarray was used to test breast cancer samples and cell lines, a significant increase in expression of EGFR1 was found in HER2-enriched TNBC as opposed to HER2-enriched/non-TNBC, which indicates that HER2-enriched tumors that are clinically not HER2-amplified could be governed by EGFR1.