CFTR and cyst: Both abnormal cell proliferation and cyst-filling-fluid secretion are cyclic AMP-mediated processes initiated by stimulating the Ras/mitogen-activated protein kinase (MAPK) pathway and by the activation of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel [13] and TMEM16A (anoctamin 1), which leads to transepithelial chloride secretion [14] (Figure 1).