Main Points of diagnsis and differentiate diagnosis in benign diseases or lesions of the breast ZHANG Na, ZHANG Bin. Liaoning Province Tumor Hospital, Shenyang 110043, China Abstract Cystic hyperplasia, mammary duct ectasia （plasma cell mastitis）, milk cyst and fat necrosis were common benign non-neoplasm lesions of the breast. Among the benign neoplasms, adenofibroma （fibroadenoma） and intraductal papilloma were much more frequency. There are several benign breast diseases such as mammary duct ectasia, fat necrosis, sclerous adenosis and massive adenofibroma need differentiate from malignant lesions of the breast. Papillomatosis and atypical hyperplasia （grade 2 and 3）belong to premalignant lesions of the breast. Up to now, there are no evidence of the relationship between cystic hyperplasia of the breast and developing breast cancer.