To study Professor Zhou Zhongying's clinical experience in the treatment of breast cancer.Methods:Medcase was employed to analyze the breast cancer cases treated by Professor Zhou Zhongying with the frequency counting method，on the basis of which the rules of syndrome differentiation and treatment were mined.Results:This study involved 316 cases，1 664 visits，429 clinical symptoms，181 disease causes，344 drugs，and 10 categories of drugs.Conclusion:Professor Zhou believes that breast cancer is caused by the combination of deficiency in the body and excess pathogen on the body，and the disease mainly attacks the liver and kidney，involving the spleen，stomach，and other viscera.Most of the patients showed the syndromes of qi and yin consumption and liver and kidney deficiency.Heat-clearing herbs and qi-replenishing and yin-nourishing herbs were commonly used for treating breast cancer.The frequency of pathogen-dispelling herbs was higher than that of healthy qi-reinforcing herbs.