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Background: The CDH1 gene codes for the epithelial-cadherin (E-cad) protein, which is embedded in the plasma membrane of epithelial cells to form adherens junctions. E-cad is known to be essential for maintaining the integrity of epithelial tissues, and the loss of E-cad has been widely considered a hallmark of metastatic cancers enabling carcinoma cells to acquire the ability to migrate and invade nearby tissues. However, this conclusion has come under scrutiny., Methods: To assess how CDH1 and E-cad expression changes during cancer progression, we analyzed multiple large transcriptomics, proteomics, and immunohistochemistry datasets on clinical cancer samples and cancer cell lines to determine the CDH1 mRNA and E-cad protein expression profiles in tumor and normal cells., Results: In contrast to the textbook knowledge of the loss of E-cad during tumor progression and metastasis, the levels of CDH1 mRNA and E-cad protein are either upregulated or remain unchanged in most carcinoma cells compared to normal cells. In addition, the CDH1 mRNA upregulation occurs in the early stages of tumor development and the levels remain elevated as tumors progress to later stages across most carcinoma types. Furthermore, E-cad protein levels are not downregulated in most metastatic tumor cells compared to primary tumor cells. The CDH1 mRNA and E-cad protein levels are positively correlated, and the CDH1 mRNA levels are positively correlated to cancer patient's survival. We have discussed potential mechanisms underlying the observed expression changes in CDH1 and E-cad during tumor progression., Conclusions: CDH1 mRNA and E-cadherin protein are not downregulated in most tumor tissues and cell lines derived from commonly occurring carcinomas. The role of E-cad in tumor progression and metastasis may have previously been oversimplified. CDH1 mRNA levels may serve as a reliable biomarker for the diagnosis of some tumors (such as colon and endometrial carcinomas) due to the marked upregulation of CDH1 mRNA in the early stages of tumor development of these carcinomas., (© 2023. The Author(s).)