One of the subgroups proposed is the so-called basal-like group of tumours, which are associated with breast cancers that express neither oestrogen receptor (ER) nor human epidermal growth factor receptor (HER)2, but express frequently 'basal' cytokeratins (CKs) such as CK-5/6, CK-14 and CK-17. This evidence concerns the gene KRT5 and breast cancer.