Background: Papillary carcinoma of the thyroid gland (PTC) constitutes the most common form of thyroid cancer and the most common endocrine malignant tumor. It is often difficult to differentiate PTC from benign papillary hyperplasia of the thyroid gland based on their morphology. Cell proliferative activity is one of the important factors for assessing the biological behavior of carcinoma. At present, the most useful marker to evaluate cell proliferative activity is Ki-67, which is expressed in all cells except those in the G0 phase. Objective and Design: Main objective of this retrospective cross-sectional descriptive study was to evaluate immunohistochemical expression of ki-67 in thyroid cancer especially papillary type among Sudanese patients. Material and Methods: A total of 60 paraffin-embedded formalin-fixed tissue specimens from thyroid lesions were included in thisstudy and stained by H&E and immunohistochemistry. Results: About 83.3% of the cases expressed Ki-67 (most of them were PTC) while only 16.7% of the cases were negative (P value is statically significant p<0.002). Conclusion: It can be concluded that using of Ki- 67 as a diagnostic marker is helpful in diagnosis of papillary thyroid carcinoma.
