Parental cell lines were chosen to represent different molecular subtypes of breast cancer and included MCF-7 and ZR-751 cell lines (ER+, PgR+, HER2-), which are hormone-dependent, and the MDA-MB-231 cell line, which is triple negative (ER-, PgR-, HER2-) and consequently hormone-independent. Here, ERBB2 is linked to breast cancer.