Comparison of measurement of surviving tumor cells by growth and clonogenic assays

Objective To compare the effect of growth and clonogenic assays in measurement of surviving tumor cells after radiation. Methods The surviving cell number and surviving fraction (SF) of MCF 7 and Colo 205 cell lines following irradiation with 2,4,and 8 Gy were measured by using Courtenay Mills clonogenic and growth assays. Results In the clonogenic assay group, the detected surviving tumors had a clonic function. There was no difference of radiosensitivities between Colo 205 cells living in suspension and on adherence. In growth assay group, the relative surviving index reached the lowest level at the 6 th to 9 th days after culture and the mean value was close to that by the clonogenic assay. Conclusion Two methods reflect different aspects of cell proliferation. Growth assay can provide information on early proliferation kinetic events. The great merit of Courtenay Mills assay is that it claims to quantify not only surviving cells but cells with clonogenic potential, which is presumably a clinically relevant end point.