CELL KINETIC-STUDY OF THYMIC EPITHELIAL TUMORS USING PCNA (PC10) AND KI-67 (MIB-1) ANTIBODIES

We performed an immunohistochemical cell kinetic study with monoclonal antibodies to proliferating cell nuclear antigen (PCNA)- PC10- and Ki -67 - MIB1 - on 62 thymic epithelial tumors, to evaluate whether there is correlation between the proliferation indices of the neoplastic ep ithelial cells and histological subtype, stage, and risk of relapse. T he 62 cases of thymic epithelial tumors were classified as medullary t hymoma (4 cases), composite (mixed) thymoma (17 cases), organoid thymo ma (predominantly cortical) (11 cases), cortical thymoma (10 cases), w ell-differentiated thymic carcinoma (18 cases), and poorly differentia ted thymic carcinoma (2 cases). Labeling indices were expressed as per centage of epithelial cells with positive nuclear immunostaining by ra ndom counting of 1,000 epithelial tumor cells, using an oil immersion 100X objective. PCNA labeling indices were consistently higher than th ose of Ki-67, and they correlated with each other. Well-differentiated thymic carcinoma showed higher labeling indices (3.11% +/- 3.53%) by Ki-67 antibody compared with the medullary type (0.60% +/- 0.07%) (P<. 05) but there were no statistically significant differences between th e other histological subtypes. Stage IV cases showed higher PCNA label ing indices (PCNA: 11.07% +/- 7.35%, Ki-67: 6.86% +/- 5.87%) than case s of the other stages (P<.05), but there were no statistically signifi cant differences in either labeling index between the other stages. Th e number of patients who relapsed was too small to permit meaningful c orrelation between labeling indices and relapse. Our results indicate that the differences in biological behavior of the different histologi cal subtypes of thymic epithelial tumors may be in part explained by d ifferences in tumor growth fraction. Analysis of a larger group of pat ients will be required to determine whether proliferation fraction as determined by this method can be used to predict outcome in individual cases. HUM PATHOL 27:70-76. Copyright (C) 1996 by W.B. Saunders Compa ny