GJB2 and cancer: Cx26 and Cx43 are the Cxs constitutively expressed in normal epithelial oesophageal tissue, but in most oesophageal tumours, the expression of Cx26 is absent, and the expression of Cx43 is decreased [130,131]; however, during tumour progression and the acquisition of the malignant phenotype, Cx proteins often translocate from the cell membrane into an intracellular site such as cytoplasm, which causes the number of Cxs to increase in different histological types of malignant tumours [132], and the excessive accumulation of Cxs may be related to cancer progression [133].