Analysis of the cycling and noncycling cell population of human solid tumors.

The size and kinetics of the cell population of six advanced human solid tumors were analyzed following the continuous infusion of H3-TDR for a period of 6 to 21 days. By using the labelling indices of the cells in interphase and mitosis, and the rate of label incorporation, it was found the only 10 to 40% of the tumor cell population was replicating at any given time. Fifty-five percent to 85% of the remaining cell mass eventually entered into cycle at least once. Anywhere from 5% to 40% of the cell population remained arrested in G2 or G0 in individual cases during the period of observation. The significant size of the "resting" cell compartment is undoubtedly one explanation for the relative insensitivity of advanced adult solid tumors to current cell cycle-oriented therapeutic regimens.