Background: Carcinoma breast is the one of the most common causes of cancer death among women. Early diagnosis and effective treatment of the disease are immensely important. The increasing number of options for treatment of carcinoma breast has made the prognostic evaluation of the disease even more important. Proliferation plays an important role in clinical behaviour of invasive carcinoma breast. Ki67 binding, is an objective measurement of cell proliferation which significantly aids in the management of the patients with carcinoma breast. Objectives: 1. Study of expression of Ki67 in primary breast carcinomas. 2. Correlation of Ki67 expression with the histopathological grade of breast carcinomas. Methodology: Forty modified radical mastectomy specimens received at the department of pathology, MIMS, Mandya from January 2015 to June 2016 were examined for gross and microscopic features. Immunohistochemistry was used to study the Ki67 expression. Ki67 status was correlated with tumour grade according to Nottingham modification of Scarff Bloom Richardson grading (NSBR grading. Results: Of 40 cases of carcinoma breast, 97.5% of the cases were positive for Ki67. The range of Ki67 score was 095%. Mean Ki67 in the study was 32.85%. Majority of the cases (62.5%) had high Ki67 expression. There was a significant statistical association between Ki67 expression with grade of the tumor(p value = 0.032). Conclusion: Our study data indicates that, high Ki67 expression is associated with high tumour grade. Conclusively, proliferative activity determined by Ki67 expression may reflect the aggressive behaviour of breast carcinoma. Ki67 detection provides valuable information about proliferative activity of cells therefore, it is necessary to combine this with other prognostic parameters for better evaluation of patient’s outcome as well as treatment decision.

Keywords: Immunohistochemistry; Ki67; Breast Carcinoma; Nottingham Modification of Scarff Bloom Richardson Grading (NSBR Grading).