SCN5A and breast cancer: To obtain a clearer picture of the triad, we have subdivided the review into three major sections, which are (1) the roles of Nav1.5 and nNav1.5 in potentiating the progression of breast cancer metastasis; (2) the general connection between breast cancer and the immune system; and (3) the involvements of Nav1.5 and nNav1.5 in the functionality of the immune system and the immunogenicity of nNav1.5.