BEST1 and neoplasm: This protein is expressed in the plasma membrane and forms Ca2+‐activated Cl− channels (CaCCs) by assembling as pentamers.[9] BEST1 was first identified as a pathogenic gene of Best's macular dystrophy (BMD).[10, 11] Moreover, recent studies have shown that BEST1 can regulate chloride currents in respiratory and renal epithelial cells and promote the proliferation of tumor cells.[12, 13, 14] However, at present, the function and mechanism of BEST1 in immune cells has not been thoroughly studied.