CLDN1 and cancer: In this context, it should be noted that claudins are considered to participate in cancer metastasis, depending on types of cancers (Martin et al, 2011; Tabariès and Siegel, 2017; Osanai et al, 2017; Bhat et al, 2020): for example, lower expression of claudin-1 is associated with cancer progression and invasion in some cancers, whereas loss of claudin-1 improves the patient survival in other types of the tumors.