Apoptosis and proliferative activity in thyroid tumors

To clarify the growth mechanisms of thyroid tumors, we examined apoptotic c ells in 61 thyroid tumors, consisting of 14 adenomas, 35 papillary carcinom as, 4 follicular car cinomas, and 8 undifferentiated carcinomas, using term inal deoxynucleotidyl transferase mediated deoxyuridine triphosphate digoxi genin-nick end labeling (TUNEL). The proliferative activity was also evalua ted immunohistochemically using the monoclonal antibody to Ki-67 antigen (M IB-1) in the same tumors. The apoptotic index (AI) was expressed as a perce ntage of the TUNEL-positive cells in the tumor cells, and a proliferation i ndex (PI), being the percentage of Ki-67 positive cells, was calculated for each tumor. The overall level of AI was very low in all histotypes of the thyroid tumors analyzed, the mean AI being 0.5 +/- 0.4 in adenoma, 0.4 +/- 0.3 in differentiated carcinoma, and 1.8 +/- 1.5 in undifferentiated carcin oma. The PI in the thyroid tumor subtypes was significantly lon er in adeno ma and differentiated carcinoma, at 0.5 +/- 0.7 and 1.1 +/- 0.7, respective ly than that in undifferentiated carcinoma at 14.5 +/- 3.7 (P < 0.05). Ther e was no correlation between clinicopathological factors and AI or PI in di fferentiated thyroid carcinoma. Our findings suggest that apoptosis occurs infrequently in thyroid tumors, and that proliferative activity markedly di ffers according to the thyroid tumor subtypes Moreover, the ratio between p roliferating cells and apoptotic cells may reflect thyroid tumor progressio n.