CYCS and breast neoplasm: Accordingly, cell cycle analyses using propidium iodide to quantify the amount of DNA suggest a G1/S arrest in PyMT transgenic breast tumour cells after SK4 inhibition (Fig. 2C,D), whereas apoptotic parameters such as cytochrome c release and caspase 3 activation were not affected by TRAM‐34 (Fig. S1E).