GJA1 and breast cancer: In addition, mammary tumors immunolabelled for the expression of Cx43 revealed no overt difference in the level of Cx43 in the mammary tumors of both Cre+ and Cre- mice although the expression appeared diffuse and intracellular compared to the more punctate pattern seen in the lactating mammary gland (Figure 5Aiv, 5Av, 5B).