CLDN6 and breast cancer: It is worth noting that several studies have used nude mice to establish tumor metastasis models, such as the liver metastasis model by injecting gastric cancer cells into the spleen [52] and lung metastasis model by tail vein injection of breast cancer cells [22,24] to observe the effect of CLDN6 on tumor metastasis, and obtained results consistent with the in vitro experiments, which profoundly demonstrated the effect of CLDN6 on tumor metastasis.