Micronuclear Assay in Breast Aspirate Smears and its Diagnostic Utility in Borderline Cases

Background: Micronucleus (MN) is the chromosomal fragment that is left out of daughter nuclei during cell division. These are round to oval in shape with a diameter ranging from 1/3rd to 1/6th of main nucleus. It serves as a bio-marker for genotoxicity. Aim: To score the micronucleus score in benign, hyperplastic lesions and duct cell carcinomas of breast and use the micronucleus score as an additional criteria for classification of borderline and false negative cases. Objectives: 1. To study the age wise and sex wise incidence of various breast lesions.2. To compare the frequency of micronuclei in various benign, hyperplastic lesions and various grades of infiltrating ductal carcinomas. Study Design: This is a retrospective descriptive study. Material and Methods: Analysis of breast cytology smears received over a period of 2 years was done. Micronucleus scoring was done by counting the number of micronuclei in 1000 epithelial cells under oil immersion and compared in various breast lesions, and in the three grades of infiltrating ductal carcinomas. Statistical Analysis: The data was analyzed using SPSS version 22 was used for data analysis and compiled with the help of tables. The analysis was reported as mean, standard deviation, sensitivity and specificity. Results: Of the 215 cases, the average statistically significant (P less than 0.05) micronuclei scores of the benign (168), adenosis (05), usual (02) /atypical (11) hyperplasia, grade 1, 2, and 3 carcinomas (29) were 0.5, 2, 2.6, 6.8, 12.5, 19.48, and 26.8, respectively. Micronucleus score of ?1 had a high sensitivity (96%) and specificity (98%) in confirmation of benign cases. Micronucleus score of ?5 and ?10 had a moderate sensitivity (73%) but a high specificity of 97% in detecting atypical ductal hyperplasia. Micronucleus score of ?10 had a high sensitivity (97%) and specificity (99%) of detecting carcinomas. Conclusion: Micronucleus scores showed a gradual and steady increase among all the categories proving the gradual occurrence of genomic damage. Therefore micronucleus score serves as an additional tool for the diagnosis of breast lesions.