Response of cell populations in tumor cords to a single dose of cyclophosphamide or radiation.

We have examined tumor cords of hepatoma 3924A in rats treated by 15 Gy of X-rays or 150 mg/kg of cyclophosphamide. Parameters measured were: cord thickness, cellular density, [3H]-TdR LI, MI and proportion of necrotic cells within the cord. With cyclophosphamide, a drop in cell density of 40% and in LI of 60% did not cause shrinkage of the cords. During the recovery phase, increase in cell number coincided with changes in the kinetics of the cell population adjacent to the capillary. For X-rays an approximately 10% decrease in cord thickness was associated with a rapid reduction in cell density and a relatively poor proliferative response of the cells adjacent to the vessel. There was little evidence for the sparing of remote cells with either agent. It did not appear that the progression of cells across the cord would be interrupted sufficiently for any 'spared' remote cells to participate in the therapeutic response.