Flow cytometric data has been collected at UTMDACC since 1988 for the purpose of calculating cell kinetic properties of human tumors in vivo. Currently the pretreatment potential doubling time, Tpot of tumors is under study here and elsewhere as a predictive assay for the treatment of squamous cell carcinomas of the head and neck by radiotherapy and of colorectal tumors by combined radiotherapy and chemotherapy. The potential doubling time is obtained from measurements by bivariate flow cytometry. Tumor cells synthesizing DNA are labeled using a halogenated thymidine analogue, either bromodeoxyuridine or iododeoxyuridine, and sampled several hours later. The presence of the thymidine analogue in a cell may be detected by fluorescently labeled monoclonal antibodies and the cell's DNA content analyzed simultaneously. Since the position of the labeled cells with respect to the cell cycle was known at the time of labeling, knowing the position of the labeled cells at the time of sampling provides information for the kinetics of the labeled population. However, the calculations used to obtain Tpot assume that only a single population of cells exists, whereas typical tumors contain multiple populations with differing DNA contents, including cycling cells with a diploid DNA content. Little is known about the kinetic behavior of these mixed populations which can include normal cells, diploid tumor cells and aneuploid tumor cells. Should their separate DNA distributions overlap, incorrect values of Tpot may be obtained. The proposed research will extend mathematical methods developed for the analysis of multiple populations to the assessment of the confounding effects of the diploid cells. This project will have the following specific aims: (1) To develop mathematical models to obtain values of Tpot corrected for multiple populations of cells with different DNA contents. (2) To validate these studies with data obtained from multiple time measurements in murine tumor systems and to examine the results obtained from measurements made at a single time as are obtained clinically. (3) To examine the effects of these diploid cells in predicting the clinical response of human tumors to therapy.