Pregnancy associated (PA) breast cancer is defined when diagnosed during pregnancy or within one year afterwards. To analyze the prognostic factors related to this disease and assess the impact of pregnancy on breast cancer patients, 88 PA breast cancer patients initially treated in the Shanghai Cancer Hospital from 1957 to 1990 were reviewed. A non-PA group including 176 patients individually well matched to the PA group was also analyzed. Univariate analysis suggested prognostic value for clinical tumor size, TNM stage, and breast feeding time among the classic prognostic factors, pregnancy associated factors and treatment modalities were evaluated. Multivariate analysis demonstrated clinical tumor size, TNM stage and axillary lymph node metastasis as independent prognostic factors. Compared with the non-PA group, the PA group was significantly correlated with delay at diagnosis, large size of the tumor, late TNM stage, extension to the skin or chest wall and administration with oophorectomy. The overall survival rates of 5-year, 10-year and 20-year were 40.39%, 36.29% and 30.70%, respectively, which were worse than those in the non-PA group, but did not reach a significant difference (p=0.0536). We are conducting further basic research to analyze the biologic characteristics of PA breast cancer.