Based on mRNA expression data, a comprehensive screening for five connexin isotypes, GJA1/Cx43, GJA3/Cx46, GJB2/Cx26, GJA6/Cx30 and GJB1/Cx32 was performed at the protein level in normal pre-menopausal breast glands and in a cohort of cancers representing all grades and major breast cancer subtypes. This evidence concerns the gene GJB1 and cancer.