multi-drug resistance against second-line medication and microrna plasma level in metastatic breast cancer patients

Background: circulating micrornas (mirnas) can help to predict the chemotherapy response in breast cancer with promising results. the aim of the present study was to investigate the relationships between the mir-199a, mir-663a, and mir-663b expression and chemotherapy response in metastatic breast cancer patients.methods: this study is a case-control study performed at yasuj university of medical sciences (2018-2021). the expression levels of mir-663a, mir-663b, and mir-199a in the serum of 25 patients with metastatic breast cancer versus 15 healthy individuals were determined by the real-time polymerase chain reaction method. the response to treatment was followed up in a 24-month period. all patients were treated with second-line medications. two or more combinations of these drugs were used: gemcitabine, navelbine®, diphereline®, xeloda®, letrozole, aromasin®, and zolena®. statistical analyses were performed in spss 21.0 and graphpad prism 6 software. the expression levels were presented as mean±sd and analyzed by student’s t test.results: the results and clinicopathological features of patients were analyzed by t test. the statistical analysis showed that mir-663a expression was related to human epidermal growth factor receptor 2 (her2) status and was significantly lower in the her2+ than her2- group (p=0.027). moreover, the expression of mir-199a and mir-663b was significantly correlated with the response to treatment, in which the expression of mir-199a was higher in the poor-response group (p=0.049), while the higher expression of mir-663b was seen in the good-response group (p=0.009).conclusion: these findings state that the high plasma level of mir-199a and the low plasma level of mir-663b may be related to chemoresistance in patients with metastatic breast cancer.