Changes in genetic constitution of an individual leads to uncontrollable cell growth and tumour formation. The acquisition of genomic instability predisposes cells to accumulate stable genome mutations causing carcinogenesis. The cytokinesis-block micronucleus cytome assay (CBMN), a well-established marker assay for chromosomal mutagen sensitivity, was applied in this study enrolling breast cancer patients and age and sex-matched controls. This work aimed to assess the predictive value of the frequency of genotoxic markers in peripheral blood lymphocytes for the risk/susceptibility of breast cancer. Samples from a hundred untreated breast cancer patients and age and sex matched controls were enrolled in the study from Government Medical College, Alappuzha. The genomic instability was assessed using cytokinesis block micronucleus assay where cytome events were marked. The results showed a significant increase in the frequency of micronucleus, nucleoplasmic bridge, and buds in the binucleated cells of breast cancer patients compared to the control samples. The variability was assessed by CBMN Cyt assay. The frequency of Micronuclei and Nucleoplasmic buds was significantly higher in the patient groups than in the controls (p < 0.0001). In Breast cancer patients, the median (IQR) range of MNi was 12(6), the Nucleoplasmic bridge 3(3) and the Nuclear buds were 2(1) and, in the controls, it was 6(5), 1(2) and 1(1) respectively. A larger difference in the frequency of genetic markers in cancer patients over control cases support a significant role of these markers in the population screening of individuals at high risk of cancer. Communicated by Ramaswamy H. Sarma. © 2024 Elsevier B.V., All rights reserved.