To determine whether HMGA1 signalling is an important oncogenic event in basal-like breast tumours, we generated an inducible cellular system for HMGA1 silencing based on short hairpin RNA (shRNA) in the oestrogen receptor-negative basal-like human breast cancer cell line MDA-MB-231 and checked for HMGA1 down-regulation after induction (Supplementary Fig. S1). Here, HMGA1 is linked to breast cancer.