Circulating miR-21 is Down-Regulated Following Adjuvant Chemotherapy in Breast Cancer Patients

Breast cancer is one of the most prevalent known cancers in women with the incidence rate of annually 7000 cases in Iran. MicroRNAs (miRNAs) are a group of non-coding RNAs with 20-25 nucleotides length, which can effect on cancer development. There is low information about the influence of anti-cancer drugs on the expression levels of miRNAs. The present study is the first investigation to evaluate the down-regulation of circulating microRNA-21 (miR-21) expression in breast cancer patients after treatment with Doxorubicin and 5-fu drugs. The expression levels of miR-21 in paired blood plasma samples of 40 new cases of breast cancer patients, were analyzed by Real-Time Polymerase Chain Reaction (RT-PCR) with 2 repeats for each sample. miR-21 rates were evaluated before and after the treatment with Doxorubicin and 5-FU medicines and data were analyzed using t-test. Comparisons between plasma miRNAs before and after the chemotherapy suggested that the treatment has down regulated the circulating miR-21 expression in both HER2+ (Human Epidermal growth factor Receptor 2 positive) and HER2-breast cancer patients. According to the obtained results, it can be suggested that Doxorubicin and 5-FU drugs significantly decrease the circulating miR-21 expression, which might play a key role in anti-tumor effects (0.15 Fold change, P-value < 0.0001).