Multidrug Resistance Associated Genes MRP1, MRP2 and MRP3 in Primary and Anthracycline Exposed Breast Cancer

Background: Multidrug resistance associated proteins MRP1, MRP2 and MRP3 confer in vitro multidrug resistance. We investigated their role in breast cancer resistance to anthracycline-based chemotherapy. Materials and Methods: Using real-time reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC), the expression of MRP1 - 3 was quantified in nine breast cancer cell lines and 30 breast carcinoma samples. Results: MRP1 - 3 mRNA was detectable in all breast cancer cell lines and tumor samples. No increase of expression was detected between untreated carcinoma and post-neoadjuvant anthracycline treatment tumor samples. IHC failed to detect the proteins. MRP1 - 3 expression was not associated with tumor response to treatment or with outcome. Conclusion: MRP1 - 3 are expressed in breast cancer cells, but are not detected with IHC. We have found no evidence linking these proteins to clinical drug resistance in a small but well-documented series of breast cancer samples.