Abstract: Objective To study the role of TTF1 and Ki-67 in thymic epithelial tumors(TET)and their relevance.Methods Fifty-nine cases of TET were collected.The pathologists were agreed on 51 cases,disagreed 8 cases,4 of which were involved with type AB.Immunohistochemistry was used to detect TTF1 and Ki-67 expressions in 51 TET with unanimous diagnosis and 30 thymic hyperplasia tissues.The correlations of TTF1 and Ki-67 expression in TET and clinical pathologic characteristics were statistically analyzed.Results Among the disagreed cases,4 of 8 were involved with type AB.There were significant differences of TTF1 and Ki-67 expressions between hyperplasia tissues and TET.Only 11 of 15 type AB expressed TTF1.The expression of TTF1 had positive correlation with World Health Organization classification(WHO)in TET.Ki-67 labeling index increased from type A to thymic carcinoma and its expression range of type A and thymic carcinoma did not overlap each.Ki-67 labeling index was correlated with WHO and clinical stages in TET.Furthermore,the expression of TTF1 had no correlation with Ki-67 in TET.Conclusion TTF1 is a highly specific marker for type AB.Ki-67 is useful for distinguishing type A from thymic carcinoma and guiding treatment by predictive value.

Key words: TTF1, Ki-67, TET, WHO classification, MasaoKa stage