Quantitative determination of disseminated tumor cells by [3H]thymidine incorporation in vitro and by agar colony formation.

A new microradioassay for the detection and quantification of disseminated tumor cells in blood and organ samples of tumor-bearing animals has been worked out in a murine total system for tumor metastasis. In contrast to previous prelabeling or in situ labeling procedures, the basis of this assay is a postlabeling in vitro of tumor cell-containing material with [3H]thymidine. Percoll gradient fractionation and autoradiography revealed that most of the isotope was incorporated into tumor cells. Titration curves with tumor cells from tissue culture were run in parallel and allowed to calculate from the radioactivity of a sample that actual number of proliferating tumor cells. The postlabeling assay correlated fairly well with an agar colony test which measure the clonogenic or stem cell potential of a tumor cell population. About 70% of syngeneic animals which had been inoculated s.c. with ESb tumor cells showed increased [3H]thymidine uptake in their blood, particularly at certain time intervals (11 and 21 days). None of these animals lived for more than 2 days longer. The advantages of the new microradioassay and its possible prognostic significance will be discussed.