Abstract
In cancer, the level of expression of breast cancer resistance protein (BCRP/ABCG2) can vary depending on cell type. However, its precise role in breast cancer has been controversial. The aim of this study was to investigate the expression of ABCG2 in breast carcinomas and relate the results to the established prognostic factors. An immunohistochemical study was conducted on 200 breast carcinoma specimens using the avidin-biotin peroxidase method. ABCG2 was expressed in 77% of cases of invasive ductal carcinoma. There was a statistically significant correlation between ABCG2 expression and each of the tumor grade, clinical stage, lymph node metastasis, and HER2 immunostaining, but no such association with progesterone receptor (PR) and estrogen receptor (ER) status. Increased expression of ABCG2 in invasive ductal carcinoma cells and its statistically significant correlation with HER2 expression are strongly correlated with tumor progression, invasion, and metastasis in human breast cancer and indicates that ABCG2 can be used as a target for the development of novel therapies.