For example, CLDN1, CLDN3, CLDN7, CLDN16 and CLDN20 have been found to be downregulated in breast cancer, and the downregulation of these claudins appearing to be linked to a more aggressive phenotype and with poor clinical outcome [1,2,3,4,5,6,7,8]. The gene discussed is CLDN1; the disease is breast carcinoma.