Immunohistochemical Assessment of Ki-67 Expression in Adenoid Cystic Carcinoma of the Salivary Glands

Objective Adenoid cystic carcinoma (ACC) is a rare malignant tumor originating from the salivary glands. It’s rather bland histological appearance that masks its ultimate biological aggressiveness. Evaluation of cell cycle and mitoses have been useful in predicting malignancy in many tumors. Ki-67 antigen is a human nuclear antigen that presents during all active phases of cell cycle. The aim of this study was to estimate whether the Ki-67 expression ratio in ACC correlated with the morphological growth pattern and tumor histological grade. Material and Methods Tissue samples of 19 ACC, collected from the files in archive of Department of oral pathology, Mashhad Dentistry Faculty. All Samples originated from minor salivary gland including 11 men and 8 women with an avarage age of 46. One section have been  stained with H&E to confirm the diagnosis and the other with Ki - 67 monoclonal antibody. All samples graded and scored for Ki-67 immunoreactivity, then the ratio of Ki-67 positive cells was calculated. Results The most incidence of tumor was in 4 and 5 decades and in women. The most common site of tumors was palate. Ki-67 expressed in 68% of all samples. The Ki-67 immunoreativity ranges from 15% to 85%. Although the avarage percentage of Ki-67 expression seems to increase with histological grade, but the difference between grade III and grade I, and between grade III and mixed I / II was not statistically significant (P value = 0.3). Conclusion For ACC, Ki-67 immunostaining regarding to histological grading is not a reliable tool in predicting the intensity of tumor aggressiveness and seems to have less value. Further studies with greater series of samples are needed to confirm this issue.