Breast ductal epithelial atypical hyperplasia is classified as mild, moderate, or severe depending on the depth of infiltration. Generally speaking, about 60%-70% of atypical hyperplasia can become cancerous. 1. Mild atypical hyperplasia: the lesion only involves the lower 1/3 of the epithelium, most of which is caused by inflammatory stimulation, and can return to normal after eliminating the triggers, and its cancer rate is basically zero. 2. Moderate atypical hyperplasia: it refers to the lesion involving the lower 1/3~2/3 of the epithelium, most of which is also caused by benign lesions, and most of which can be recovered after removing the triggers; a small part of it is more serious, and about 30% of it may be cancerous. 3. Severe atypical hyperplasia: it refers to the lesion involving the whole epithelium, i.e. carcinoma in situ. This condition is difficult to be reversed and usually does not recover even after eliminating the triggers, and the chance of cancer is close to 100%. Therefore, if atypical hyperplasia of breast ductal epithelium occurs, you should go to the hospital in time and take treatment under the guidance of doctor.