A comparison of the patterns of laminin expression in fibroadenoma, fibrocystic diseases, pre-invasive and invasive ductal breast carcinoma

The basement membrane (BM), of which laminin is a major glycoprotein component, is an important barrier to tumour cells which must be breeched before metastatic spread can occur. We have compared the pattern of laminin expression in a range of benign and malignant breast lesions to better understand the process of tumour progression. A total of 162 cases of breast samples, comprising 18 fibroadenomas, 22 cases of fibrocystic disease, 96 cases of invasive ductal carcinoma and 26 carcinomas with intraductal components, were evaluated for laminin expression by a standard immunoperoxidase method on formalin-fixed, paraffin-embedded histological sections, using a commercial antibody against human laminin. The pattern of laminin expression was charted as follows: Type I, > 70% of BM complete/continuous; Type II, > 70% of BM moderately disrupted; Type III, > 70% of BM completely disrupted. The Type I pattern was observed in all cases of fibroadenoma and fibrocystic diseases, and in 77% of intraductal carcinoma components. Various patterns of BM disruption were observed in invasive ductal carcinoma. Severity of BM disruption correlated with histological grade of the carcinomas (P < 0.001). Small-sized tumours, those without lymphatic invasion and lymph node-negative tumours showed more complete patterns of laminin expression. The current study suggests that tumour cells with high histological grade possess an enhanced capacity to disrupt the basement membrane, an important step in the metastatic process. The detection of BM disruption by immunohistochemical staining for laminin is technically easy and may be usefully applied for the differentiation of in situ and microinvasive carcinoma.