Correlation between ki-67 labeling index and mitotic index in oral squamous cell carcinoma Archana Buch, Niladri Haldar, Supriya Kheur, Shirish Chandanwale, Harsh Kumar Clinical Cancer Investigation Journal 2019 8(3):90-95 Background: Oral squamous cell carcinoma (OSCC) is the most prevalent type of oral cancer. Counting of mitotic figures as well as the detection of Ki-67 expression by immunohistochemistry have been used to detect cell proliferation in malignant tumors. We correlated Ki-67 expression with mitotic activity and observed any notable relationship between them, to ascertain the role of Ki-67 protein as a tumor proliferative marker in OSCC. Subjects and Methods: A cross-sectional study was undertaken at a tertiary care hospital in Western Maharashtra over a period of 2 years. Fifty paraffin blocks of patients diagnosed as OSCC were included in our study, who were classified into well-differentiated squamous cell carcinoma (n = 24), moderately-differentiated squamous cell carcinoma (n = 23), and poorly differentiated squamous cell carcinoma (n = 3). Two slides per case were stained with H and E and Ki-67 marker, then observed under light microscopy to obtain Mitotic Index (MI) and Ki-67 Labeling Index (LI), respectively. Results were analyzed using mean, standard deviation, Chi-square test, and unpaired t-test. Results: Hyperplastic epithelium revealed higher Ki-67 LI as compared to normal epithelium. There was a statistically significant (P = 0.045) increase in Ki-67 LI in the proliferating margin with grade of OSCC. Positive linear correlation was noted between Ki-67 and MI in tumor proper (r = 0.186) and proliferating margin (r = 0.337) and was statistically significant in the latter (P = 0.017). Conclusions: Ki-67 LI can reliably detect the proliferative potential of cells at the invasive margin of a tumor. MI, on the other hand, can detect the cell proliferation rate of the tumor that is in correlation with the histopathological grade of OSCC.