Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 51 12 2022 12 17 2808 2816 Esmat Ghalkhani Department of Medical Genetics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Mohammad Taghi Akbari Department of Medical Genetics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Pantea Izadi Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Habibollah Mahmoodzadeh Iran National Tumor Bank, Cancer Institute of Iran, Tehran University of Medical Sciences, Tehran, Iran Fatemeh Kamali Department of Surgery, Cancer Institute of Iran, Tehran University of Medical Sciences, Tehran, Iran 2019 09 03 2019 12 09 Background: A significant part of deaths related to breast cancer is the result of invasion to other organs. It is essential to discover new non-invasive biomarkers to improve anticipation of recurrence risk in breast cancer patients. In this study, the plasma levels of miR-129 and miR-203a were evaluated to investigate their diagnostic potential in breast cancer and its metastasis. Methods: In this case-control study, conducted in Tarbiat Modares University, Tehran, Iran, in 2019, Invasive Ductal Carcinoma blood samples were divided into 3 groups based on their stages as I, II/III, IV. Each group contained 30 individuals. We also recruited 30 normal individuals as a control group. Real-Time PCR was conducted to evaluate miR-129 and miR-203a expression levels. The discriminatory ability of the evaluated plasma miRNAs was assessed by ROC (Receiver Operating Characteristic) curves in breast cancer diagnosis and its metastasis. Results: MiR-129 and miR-203a expression levels were significantly downregulated in breast cancer. Reducing tendency was observed in the mentioned miRNAs from less to more invasive stages. The expression level of miR-129 was decreased in metastatic than non-metastatic patients and it was significantly related to metastasis. A significant association between miR-129 expression level and lymph node status was also observed (P=0.04). Evaluation of ROC curves revealed that miR-129 and miR-203a were able to discriminate breast cancer fairly and poorly respectively. The ability of miR-129 in the diagnosis of breast cancer metastasis was poor. Conclusion: MiR-129 and miR-203a may both act as tumor suppressor miRNAs. Our results need further evidence in a large population to be confirmed as diagnostic markers.  https://ijph.tums.ac.ir/index.php/ijph/article/view/18241 https://ijph.tums.ac.ir/index.php/ijph/article/download/18241/7812