190 Neoplasma 2021; 68(1): 190–199 doi:10.4149/neo_2020_200225N185 Association study of miR-22 and miR-335 expression levels and G2 assay related inherent radiosensitivity in peripheral blood of ductal carcinoma breast cancer patients Narjes BAKHTARI 1 , Hossein MOZDARANI 1, *, Mahdieh SALIMI 2 , Ramesh OMRANIPOUR 3 1 Department of Medical Genetics, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran; 2 Department of Medical Genetics, Medical Biotechnology Institute, National Institute of Genetic Engineering and Biotechnology, Tehran, Iran; 3 Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran *Correspondence: mozdarah@modares.ac.ir Received February 25, 2020 / Accepted June 2, 2020 Identifying patient’s cellular radiosensitivity before radiotherapy (RT) in breast cancer (BC) patients allows proper alternations in routinely used treatment programs and reduces the adverse side efects in exposed patients. Tis study was conducted on blood samples taken from 60 women diagnosed with Invasive Ductal Carcinoma (IDC) BC (mean age: 47±9.93) and 30 healthy women (mean age: 44.43±6.7). Te standard G2 assay was performed to predict cellular radio- sensitivity. To investigate miR-22 and miR-335 expression levels in peripheral blood mononuclear cells (PBMCs), qPCR was performed. Te sensitivity and specifcity of the mentioned miRNAs were assessed by plotting the Receiver Operating Characteristic (ROC) curve. Binary logistic regression was performed to identify the miRNA involvement in BC and cellular radiosensitivity (CR) of BC patients. Te frequency of spontaneous and radiation-induced chromatid breaks (CBs) was signifcantly diferent between control and patient groups (p<0.05). A cut-of value was determined to diferentiate the patients with and without cellular radiosensitivity. miR-22 and miR-335 were signifcantly downregulated in BC patients. miRNAs expression levels were directly associated with CR. ROC curve assessment identifed that both miRNAs had acceptable specifcity and sensitivity in the prediction of BC and CR of BC patients. Binary logistic regression showed that both miRNAs could also predict BC successfully. Although only miR-22 was shown potent to predict CR of BC patients, both miR-22 and miR-335 might act as tumor suppressor miRNAs in BC. miR-22 and miR-335 may be promising potential biomarkers in BC prediction along with other important biomarkers. Moreover, mirR-22 might be a potential biomarker for the prediction of CR in BC patients. Key words: breast cancer, G2 assay, cellular radiosensitivity, miR-22, miR-335 Breast cancer (BC), is the most common type of cancer among women and the frst cause of cancer-related mortality in women worldwide [1]. Radiotherapy (RT) is a common method used for the treatment of ~50% of all cancer patients in some stages of their disease [2]; however, some patients are over/undertreated afer RT [3]. Radiosensitivity means the relative sensitivity of normal cells, tissues, or organs to the efects of ionizing radiation [4]. Cellular radiosensitivity depends on several factors including the type of radiation, the DNA repair capacity, etc. [5]. Identifying radiosensitive patients before performing RT allows a proper alternation in routinely used treatment regimens to reduce the adverse side efects in exposed patients [4]. Radiation response analysis in diferent subtypes of breast cancer has revealed that luminal subtypes (A, B) are more sensitive to irradiation although triple negative breast cancers (TNBC) and Her2+ subtypes are almost radio-resistant [6]. Provided that distinct molec- ular subtypes of BC show a diferent response to irradiation, it might afect the clinical outcome of treatment [7]. Studies have also revealed that peripheral blood lympho- cytes from patients with diferent types of cancer show higher chromosomal abnormalities (CA) than healthy individuals afer irradiation [8]. Enhanced CA afer irradia- tion has been detected in ~40% of BC patients while only in ~10% of healthy individuals [9, 10]. G2 assay, a widely used method for the study of radiosensitivity, is in vitro irradia- tion of peripheral blood lymphocytes in the G2 phase of the cell cycle to create DNA damage, which is ofen repaired during G2 to M-phase transition, residual lesions can be observed and measured at metaphase as CA [11]. Te high