Aims: To demonstrate immunohistochemically the alpha3 and gamma2 chain of laminin-5 in benign epithelial and malignant lesions of the human breast.
Methods and results: The alpha3 chain was identified by the monoclonal antibody BM165 and the gamma2 chain by GB3 in shock frozen samples using APAAP (alkaline phosphatase monoclonal anti-alkaline phosphatase) technique. The pre-existing breast epithelium, the 12 benign ductal and lobular proliferations and the three fibroadenomas showed a continuous immunostaining in the basement membrane region. In contrast to benign epithelial lesions, the 44 cases of invasive breast carcinoma showed a loss of the laminin-5 chains in more than 50% of the carcinoma stroma interface. Twenty-four out of the 44 invasive carcinomas revealed a complete loss of laminin-5 immunostaining. Focal defects of the laminin-5 immunostaining were also found in ductal carcinoma in situ in its pure form.
Conclusions: As recently described, the malignant transformation of breast epithelium with expression of an invasive phenotype is associated with a decrease of hemidesmosomes. The reduced immunostaining of laminin-5 is in line with this finding because laminin-5 represents the major component of the anchoring filaments attaching hemidesmosomes to the basement membrane. We feel that immunohistochemical demonstration of laminin-5 may serve as a marker of benignity in epithelial breast lesions. While other carcinoma types exhibit an increased laminin-5 deposition, which has been suggested as an invasion promoting factor, the loss of laminin-5 in breast cancer supports the view that breast carcinomas do not utilize laminin-5 for invasion.