Clinical application of the thymidine incorporation assay

An improved method for testing human tumors against chemotherapeutic agents was developed. Drug effects were quantitated in the thymidine incorporation assay (TIA) by measuring inhibition of deoxyribonucleic acid (DNA) synthesis by the proliferating cell population following exposure to anticancer drugs. Results were obtained within five days. A total of 480 out of 568 tumors received were evaluable for an overall growth rate of 85 percent. Even small biopsy specimens could be successfully grown. In 126 correlations with clinical response, the TIA had a prediction accuracy for sensitivity of 51 percent and a prediction accuracy for resistance of 97 percent. Because it is rapid, has a high growth rate, and is not subject to clumping and other cellular artifacts, the TIA represents a significant improvement over colony counting assays for predicting drug effects in human tumors.