ERBB2 and breast carcinoma: In order to facilitate identification of molecular programmes central to breast cancer cell quiescence irrespective of molecular sub-type, we expanded our established in vitro model system to incorporate a panel of cell lines that broadly represent the main types of human breast tumour; MCF-7 (luminal), SK-BR-3 (HER2-enriched), MDA-MB-468 (basal-like) and MDA-MB-231 (claudin-low) (Figure 1A).