Objectives: To investigate the role of expression of multidrug resistance gene (mdr-1 gene) in chemotherapeutic resistance of breast cancer and to determine if expression of mdr-1 gene may act as an index for predicting chemotherapy response and prognosis.
Methods: Using reverse transcription-polymerase chain reaction (RT-PCR) technique, we determined the levels of mdr-1 mRNA in 82 breast cancer samples.
Results: Positive expressions of mdr-1 gene were 34.3% in 35 cases of untreated primary breast cancer and 59.0% in 47 cases of relapsed metastatic breast cancer, separately, and the difference was statistically significant (P < 0.05). In 28 cases of relapsed metastatic breast cancer of mdr-1 gene positive expression, 22(78.6%) were ever treated with MDR related drugs. Levels of mdr-1 gene expression of all 7 cases were higher after chemotherapy than before chemotherapy. Positive expressions were 16.7% and high grade positive expressions were 5.6% in 18 sensitive cases. Positive expressions were 71.4% and high grade positive expressions were 50.0% in 14 resistant cases. The difference was statistically significant (P < 0.01). There were no relations between expression of mdr-1 gene and ages, menopause status, lymphnode involvements, clinical stages, and estrogen receptor levels.
Conclusion: The results indicated that retreated metastatic breast cancer is more extensively resistant than untreated primary breast cancer and acquired drug resistance is an important reason. Expression of mdr-1 gene seems to be a reference index for predicting response of chemotherapy.