Objective      To evaluate the clinical value of core needle biopsy (CNB) in the diagnosis of mastopathy without obvious mass.       Methods      From May to December 2011

891 patients were enrolled in the study

with the following including criteria: with breast pain and mass (asymmetrical mass or patchy glands thickening in unilateral breast); with Breast Imaging Reporting and Data System (BI-RADS) at 0 to 3 by molybdenum target mammography or color Doppler ultrasonography; with no obvious improvement after treatment with tamoxifen or Chinese herbal products. They all accepted CNB. The clinical manifestation in palpation and histopathological changes were correlatively analyzed. The patients diagnosed with atypical hyperplasia were followed up.       Results      According to the results of CNB

5 patients was diagnosed as invasive ductal carcinoma

6 intraductal carcinoma

1 malignant lymphoma

35 atypical ductal hyperplasia

and the rest were benign diseases of breast. Among these 35 patients with atypical ductal hyperplasia

22 patients accepted operation

and 11 of them were identified as invasive ductal carcinoma

5 intraductal carcinoma and 6 adenosis and atypical ductal hyperplasia. The left 7 patients refused operation and remained in the follow-up.       Conclusion      For the patients with asymmetrical mass or patchy glands thickening in unilateral breast

CNB should be performed on the patients having no obvious improvement or poor outcome after drug treatment in order to exclude breast cancer or precancerosis.