E-cadherin-mediated cell-cell adhesion prevents invasiveness of human carcinoma cells. This study demonstrates that the invasive potential of human carcinoma cells is closely related to their degree of epithelial differentiation. Well-differentiated carcinoma cells, which retain epithelial characteristics, are noninvasive and express E-cadherin, while poorly differentiated cells, which lose epithelial features, are invasive and lack E-cadherin expression. Transfection of E-cadherin cDNA into dedifferentiated carcinoma cells restored their noninvasive phenotype, indicating that E-cadherin is crucial for maintaining the differentiated, noninvasive state of epithelial cells. The loss of E-cadherin expression is associated with dedifferentiation and invasiveness, suggesting that E-cadherin acts as an invasion suppressor. E-cadherin is a 120-kD cell surface glycoprotein that plays a key role in cell-cell adhesion and is expressed in epithelial tissues. Its expression is inversely correlated with the invasiveness of carcinoma cells, as evidenced by in vitro experiments showing that E-cadherin-positive cells are noninvasive, while E-cadherin-negative cells are invasive. The study also highlights the importance of E-cadherin in tumor differentiation and its potential role in preventing tumor cell invasion in vivo. The findings suggest that E-cadherin is a valuable marker for differentiated, noninvasive human carcinoma cells and may serve as a target for therapeutic interventions aimed at preventing cancer progression.E-cadherin-mediated cell-cell adhesion prevents invasiveness of human carcinoma cells. This study demonstrates that the invasive potential of human carcinoma cells is closely related to their degree of epithelial differentiation. Well-differentiated carcinoma cells, which retain epithelial characteristics, are noninvasive and express E-cadherin, while poorly differentiated cells, which lose epithelial features, are invasive and lack E-cadherin expression. Transfection of E-cadherin cDNA into dedifferentiated carcinoma cells restored their noninvasive phenotype, indicating that E-cadherin is crucial for maintaining the differentiated, noninvasive state of epithelial cells. The loss of E-cadherin expression is associated with dedifferentiation and invasiveness, suggesting that E-cadherin acts as an invasion suppressor. E-cadherin is a 120-kD cell surface glycoprotein that plays a key role in cell-cell adhesion and is expressed in epithelial tissues. Its expression is inversely correlated with the invasiveness of carcinoma cells, as evidenced by in vitro experiments showing that E-cadherin-positive cells are noninvasive, while E-cadherin-negative cells are invasive. The study also highlights the importance of E-cadherin in tumor differentiation and its potential role in preventing tumor cell invasion in vivo. The findings suggest that E-cadherin is a valuable marker for differentiated, noninvasive human carcinoma cells and may serve as a target for therapeutic interventions aimed at preventing cancer progression.