YES1 and breast cancer: To determine whether Yes activation is sufficient to confer resistance to HER2-targeted drugs, we stably transfected BT-474 breast cancer cells (parental cells of BT-474/R1-7) and SK-OV-3 ovarian cancer cells (to assess cell specificity) with wild-type YES1 (WT) or constitutively active YES1 (Y537F), and analysed resistance to the HER2-targeted drugs.