INFLUENCE OF SAMPLING TIME ON ASSESSMENT OF POTENTIAL DOUBLING TIME

Potential doubling time (T-pot), S-phase transit time (T-s), and labeling index were determined in three experimental rodent tumors by in vivo incorporation of bromodeoxyuridine and flow cytometry. The kinetic parameters were derived from the relative movement method at varying sampling times (time between injection of bromodeoxyuridine and tumor excision). T-s and T-pot were close to the expected (extrapolated) values of the two parameters with sampling time within the range 60-100% of the expected T-s. With short sampling time, T-s and T-pot were considerably over- or underestimated. By use of the original method by (Begg et al., Cytometry 6:620-626, 1985), the T-pot came out with a twofold overestimation with a short sampling time. Generally, modified methods for calculation of T-s did not improve the results. When T-pot is measured in human tumors, there is no a priori knowledge of the kinetic parameters. Consequently, the sampling time must be based on the general experience of tumor cell kinetics in the specific tumor type measured. A relatively long sampling time should be aimed for when measuring T-pot in human tumors. With proper sampling time, T-pot assessed by flow cytometry was found to be a precise and reproducible parameter. (C) 1994 Wiley-Liss, Inc.