Ki-67 labeling index is a more reliable measure of solid tumor proliferative activity than tritiated thymidine labeling.

The proliferative activity of tumors has been shown to have prognostic significance in a variety of solid tumors. The standard method for assessing the proliferating fraction has been the measurement of the tritiated thymidine labeling index (TLI). Ki-67 is a monoclonal antibody that labels proliferating cells. In this study, the authors compared the proliferative activity of seven solid tumor specimens, using both methods simultaneously, on comparable sections from the same specimen. As expected, in every case the Ki-67 labeling index (KiLI) was greater than the TLI. The mean TLI ranged from 4.4 +/- 0.4% to 16.7 +/- 10.2%. The KiLI from these same tumors ranged from 25.7 +/- 8.6% to 41.2 +/- 12.2%. The mean coefficient of variation for measurements from different sections within the same specimen was 28.8 for TLI and 16.4 for KiLI. Therefore, KiLI shows less variability within different sections of the same specimen and is, therefore, a more reliable marker for proliferative activity than is TLI.