ERBB3 and breast cancer: To characterize the expression of heregulin (NRG1 gene) and HER3 (ERBB3 gene) in breast cancer cell line models, and select the most appropriate lines for functional experiments, we investigated the relative baseline mRNA expression levels of ERBB3 and NRG1 (α and β heregulin splice isoforms) in a large panel of breast cancer cell lines by quantitative reverse transcription-PCR (qRT-PCR).