KCNN4 and cancer: Particularly, the expression of KCa channels, including small-conductance KCa (SKCa) channels (consisting of SK1 (KCa2.1), SK2 (KCa2.2), and SK3 (KCa2.3) subtypes), intermediate-conductance (IKCa/SK4) and big-conductance (BKCa) channels in tumor cells has gained interest in the cancer field.