Serial labeling index determination as a predictor of response in human solid tumors.

A rapid method for determining labeling indices in solid tumor specimens, tumor-induced effusions, and tumor-bearing bone marrows was utilized in 116 patients. Of these, 48 patients were studied pre- and postchemotherapy. The magnitude of a significant change in labeling index (LI percent) was determined statistically. Of the 48 patients studied serially, 42 were studied 17 days or less following completion of their chemotherapy. In 26 patients without a significant change in tumor LI percent, there was no subsequent clinical response to chemotherapy. Three additional patients in this group are inevaluable at present. In 11 patients, there was a significant fall in tumor LI percent following chemotherapy. Seven of these had a 50 percent or greater regression of demonstrable disease, one patient had definite tumor effect but the effect was not a partial response and three patients were not evaluable for clinical response. In two patients there was a significant increase in tumor LI percent and the patients had rapid tumor progression and death. Predictions derived from serial study of the LI percent by this method correlate significantly with subsequent behavior of the tumors tested following chemotherapy and may prove clinically useful in making decisions about when or whether to change therapy.