KCNN4 and breast cancer: As SK4 channels are known to be important determinants in the activation of T and B cells (Begenisich et al., 2004; Kang et al., 2014; Xu et al., 2014), decreased tumour formation in SK4 KO mice may be masked by the inability of the SK4‐deficient immune system to recognize and/or control tumorigenesis in breast cancer.