Immunohistochemical detection against type IV collagen and laminin (LN) and ultrastructuraldetection of the basement membrane(BM)was performed in a total of 184 cases of breast lesions(98breast carcinomas and 91 benign lesions).Histologically

the lesions were diagnosed asadenosis

sclerrosing adenosis

epitheliosis

fibroadenoma

papillomatosis

ductal carcinoma in situand invasive carcinoma.In all benign lesions and ductal carcinoma in situ

a distinct andcontinuous BM

containig both laminin and type IV collagen was found at the epithelial stromalinterface.On the contrary

no BM deposition or only attenuated and fragmented BM could bedemonstrated in all cases of invasive cardnoma。NOrelationship between histological malignancygrade of the infiltrating ductal carcinoma and the extent of BM deposition was ob-served.Ultrastructural finding of the BM in various breast lesions were consistent with theimmunostaining results.Our study suggests that the demonstration of BM in which type IVcollagen and LN show the same result can be value in the differential diagnosis between benignbreast lesions

carcinoma in situ and invasive carcinoma BM defect is a factor for invasion to occur.