Background: Breast cancer prognostic markers and molecular subtypes reflect underlying biological tumor behavior and are important for patient management.Women in China, even in western China, are more and more likely to be prognosticated and treated based on well-characterized markers such as the estrogen receptor (ER), progesterone receptor (PR) and Her2.We conducted this study to determine the prevalence of breast cancer molecular subtypes in the western China as a procedure of underlying biological characteristics driving tumor clinical feature.Methods: To determine molecular subtypes we characterized over 11,850 cases of clinical pathologic information of breast cancer including ER, PR, Her2, p53, and Ki67 immunohistochemistry obtained from 22 center hospitals of 12 provinces in western China.Some of them without comprehensive information, so actually 8795 breast cancer cases had been analyzed by means of molecular subtype.Results: Our study demonstrated that the peak age incidence of breast cancer was between 40 and 50 years in western China.Totally, 736 patients (6.21%) were found to have a positive family history of cancer, and most of them were between the ages 35 and 65 years.It was found that 44.53% ofthe cases were luminal A, 8.36% were luminal B, 8.86% were Her2+ER-, and 17.78% were basal-like.The Luminal A subtype was more likely diagnosed in older patients and associated with favorable prognosis (lower histologic grade, smaller tumor size),was found in nearly 44.53% of cases.However, the basal-like subtype, associated with poor prognosis, was found in 17.78% of cases.These findings are in contrast to other parts of China in which the basal-like subtype is lower represented, even in some west countries.Conclusions: It is appeared that older patients were combined with higher frequency of luminal A, in contrast,the younger patients seemed with higher frequency of basal-like type.Breast cancer cases have unfavorable underlying biology in western China.These data suggest that the detection of molecular markers and early detection of breast cancer should be improved in western China.