Labeling index in clinical specimens estimated by the antinucleoside antibody technique.

The labeling index was estimated in human tumor biop sies with a new method in which antinucleoside antibody and immunoperoxidase staining are used. Excellent agree ment of the [3H]thymidine autoradiography labeling index and the antinucleoside immunoreactivity labeling index was obtained in cell aspirates from solid tumor and fluid specimens taken before radiation or chemotherapy as well as in serial tumor samples taken during therapy. The new method was also applied to biopsies of solid tumor specimens, for which the [-'HJthymidine autoradiography method is not generally applicable. Fifteen pretreatment human mammary adenocarcinomas were examined. The mean labeling index was 10.8%, in good agreement with results of others who used [3H]thymidine autoradiogra phy. Biopsies from eight patients with head and neck cancers were examined by the new method to learn whether their pretreatment labeling indices were predic tive of a good response to a combination chemotherapy regimen. Before application of antinucleoside antibody, frozen sections must be treated with ribonucleases. We found that, with some specimens, antinucleoside antibody im munoperoxidase labeling indices were spuriously higher without the ribonuclease pretreatment; probably this was due to interference from immunoreactive nuclear RNA. These results confirm previous studies with cell cultures and animal tumor models, indicating that the new method is a reliable way to estimate the proportion of cells in DNA synthesis in biopsies of human tumors. Results may be obtained in 2 hr by a relatively simple method with poten tially wide application. Correlation of pretreatment label ing indices with tumor responses to therapy and schedul ing of chemotherapy or radiation therapy after clinical synchronization of the tumor cells are some of the poten tial clinical applications.