Adenosis of breast is the proliferation of breast epithelium and fibrous tissue, sometimes accompanied by cyst formation and epithelial metaplasia into other tissue morphological characteristics. It is the early stage of mammary dysplasia. Its main changes are obvious focal hyperplasia of mammary alveoli and ductules, and different degrees of connective tissue hyperplasia. The lobular structure basically loses its normal morphology, and even the alveolar epithelial cells are scattered in the fibrous matrix. According to the development of the lesion, it can be divided into three stages: lobular hyperplasia, fibroadenosis and sclerosing adenosis. It has been reported in the literature that except for lobular hyperplasia, no cancer was found, but cancer was found in the last two stages, which has important clinical significance.