Abstract: Objective　To explore the possible role and mechanism of extracellular matrix in the invasion and metastasis of breast cancer.Methods　The expression of laminin and collagenⅣ in 50 cases of breast carcinoma and 23 axillary lymph nodes with metastasis was immunohistochemically detected.Results　By Immunohistochemical staining, the tissues of breast carcinoma showed negative reaction for collagenⅣ and laminin or positive reaction in interrupted linear pattern or fragmentary pattern, without continuous linear pattern as shown in normal tissues and benign lesions of the breast. The expressions of collagen Ⅳ and laminin were correlated with the histological grading(P<0.01), metastasis (P<0.01) and pathologic mitosis(P<0.05) of breast carcinoma, but no correlation was found between the expressions and the histological type, tumor size and intravascular cancer cell emboli. In the metastatic focus, the positive staining for laminin was observed in tumor cell cytoplasm and extracellular matrix in fragmentary pattern.Conclusion　Extracellular matrix is reducted with the tumor progression,and significantly correlated with the differentiation,metastasis and pathologic mitosis of breast carcinomas, indicating that poorly differentiated tumors with more mitosis and great potential to metastasize has stronger ability to destroy basement membranes. Some cancer cells are able to synthesize components of basement membrane, which may be responsible for the invasive activity of tumor cells.