In the current study we have expanded our investigation on the effect of chronic stimulation of Kv11.1 on the tumor suppressor p21waf/cip by testing the effect of NS1643 on molecularly different breast cancer cells representative of the following phenotype: Luminal A and p53-positive (MCF7), Luminal A and p53-negative (T47D), claudin-low breast cancer cells (MDA-MB-231) and HER2-overexpressing (SKBr3) breast cancer cells [27]. Here, ERBB2 is linked to breast carcinoma.