Role of Ki-67 as a proliferative marker in lesions of thyroid

Background: Specific criteria are used to diagnose thyroid neoplasms; however, the distinction between certain neoplasms, such as follicular adenoma and carcinoma, could be difficult. Thus, additional diagnostic features that can assist in this distinction would have great clinical usefulness.
Aims: To evaluate the role of the proliferative marker Ki-67 in nonneoplastic and neoplastic lesions of the thyroid, with a special emphasis on the distinction between follicular adenoma and follicular carcinoma.
Settings and Design: A retrospective study from a tertiary care center.
Materials and Methods: One hundred cases of thyroid lesions, including 50 nonneoplastic and 50 neoplastic lesions, were retrieved from the archives of the Department of Pathology, Pt. BD Sharma PGIMS, Rohtak, Ki-67 immunostaining was performed by peroxidase-antiperoxidase method and compared with mitotic counts.
Results: Ki-67 labeling index (LI) showed a progressive rise from multinodular goiter to benign to malignant neoplasms. A statistically significant difference was observed in Ki-67 counts between multinodular goiter vs papillary carcinoma (P < 0.05) and follicular adenoma vs follicular carcinoma (P < 0.05). The correlation between mitotic counts and Ki-67 LI was found to be significant.
Conclusions: In the present study, Ki-67 was found to be useful in differentiating between follicular adenoma and follicular carcinoma, but since the sample size of our study was small, larger studies are needed to confirm this observation as well as to assign a cutoff value for differentiating benign from malignant tumors.