Taking into account the tissue-specific expression of the claudin proteins, Jiang et al. [21] noted that they could be used as prognostic and diagnostic biomarkers, e.g., claudin-1 for colon cancers, claudin-3 for ovarian cancers, claudin-10 for hepatocellular carcinomas, etc. Thus, claudin-12 may be used as a biomarker for tumor progression and metastasis in the gastrointestinal tract, lung SqCC, and osteosarcomas. Here, CLDN1 is linked to ovarian cancer.