Age-dependent change of the effect of a cytostatic drug on the proliferation kinetics of a solid tumor of the mouse.

The aim of the present investigations was to study the effectiveness of a cytostatic drug (VCR) during different phases of tumor growth (1st, 7th, 14th days a.t.) and at the periphery and at the centre of the tumor (on the 14th day a.t.). Furthermore the inducement of a partial synchronization in the proliferation of tumor cells was attempted. It was found that the intensity of the cytostatic effect significantly decreased both with the passage of time after transplantation and within the tumor from the periphery to the centre. The changing cytostatic sensitivity probably is due to the diminishing vascular supply and the decreased rate of cell proliferation; especially the decline of the growth fraction. A partial synchronization of the proliferation of tumor cells could not be demonstrated.