New approaches to cell kinetics in human tumors

Both clinical and laboratory evidence indicate that local control rates for many experimental and clinical human tumors decrease with protraction of the overall duration of radiation therapy. A likely basis for this is tumor cell repopulation during treatment. Such observations have stimulated interest in tumor kinetics, and a number of techniques have evolved to increase the potential for meaningful clinical study of the proliferative behavior of tumors. This review discusses the clinical and experimental evidence for proliferation during treatment, describes two potential approaches--accelerated fractionation and inhibition of proliferation--that could be employed in attempting to overcome such intratreatment proliferation, explores both past and newer, evolving methods available for measuring tumor cytokinetics, and discusses how such kinetic information could be used in the future to tailor therapy to a tumor's individual characteristics.