【Abstract】 Objective To investigate the expression level of cyclin D1 protein in breast intraductal proliferative lesions and its relationship with invasive cancer. Methods From July 2006 to July 2014, a total of 180 paraffin specimens of breast tissue were selected, which met the inclusion and exclusion criteria. Immunohistochemistry was used to detect the expression of cyclin D1 protein in each tissue, and the relationship between cyclin D1 positive expression and the pathological features and prognosis of invasive breast cancer was analyzed. Results Compared with DCIS group and invasive carcinoma group, the positive expression rate of cyclin D1 protein was lower in the paracancerous group, udh group and CCL group (P＜0.05). The positive expression of cyclin D1 protein was closely related to tumor diameter, TNM stage, histological grade and lymph node metastasis in invasive breast cancer (P＜0.05). The 5year overall survival rate of cyclin D1 negative group was higher than that of cyclin D1 positive group, and the difference was statistically significant (P＜0.05). TNM stage, lymph node metastasis and cyclin D1 positive were independent risk factors for prognosis of invasive breast cancer (P＜0.05). Conclusion The expression level of cyclin D1 in breast duct proliferative lesions may be a risk factor for invasive carcinoma. The higher the expression level of cyclin D1, the greater the risk of invasive carcinoma and the worse the prognosis.