The DNA content, cellular ultrastructure and the expression of blood group Y antigen and immunosuppressive acidic protein-2(IAP-2) were observed in normal breast, cystic hyperplasia of breast and breast cancer. The results showed: the results observed in the cells of cystic hyperplasia with epithelial proliferation grade Ⅰ were similar to those in normal breast cells. The DNA content increased, the hypoplasia and dedifferentiation features in some structures of cellular membrane and nucleus were observed, and the abnormal antigens expressed in part of the atypical hyperplasic cells. The DNA content and ultrastructure in a part of cells with aypical hyperplasia grade Ⅲ were similar to those in the cells of breast cancer grade Ⅰ. The results indicated that in the couse of atypical hyperplasia, the biological abnormalities and its extent of those cells were closely related to the differentiation extent, the developing tendency and the risk of canceration of the cystic hyperplasia of breast.
