ERBB2 and breast cancer: For in vitro studies, the authors used the MCF-7 breast cancer cell line, which expresses intermediate levels of HER2 and insulin-like growth factor 1 receptor (IGF1R) and high levels of the carbohydrate antigen Lewis Y. Bispecific antibodies targeting Lewis Y, IGF1R, or HER2 were complexed with digoxigenin-Cy5 and incubated with MCF-7 cells.