Growth kinetics of a rat mammary tumour transplanted into immune-suppressed mice

The growth kinetics of a transplanted rat mammary tumour and its xenografts in immune-suppressed mice were studied using the technique of labelled mitoses. Growth of the tumour in rats was regular and uniform but when transplanted into mice the growth of the implants was irregular and generally slower. The second passage tumours in mice showed rapid and regular growth with a volume doubling time approximately half that for the tumours in the rat. Values for the G1 phase duration, intermitotic time and growth fraction were greater for the tumours in the mouse although the data for the first passage in mice were difficult to interpret. The kinetic changes between the rat and mouse hosts primarily reflect a large and variable amount of cell loss from the first passage xenografts in the mouse, with adaptation by the second passage towards reduced cell loss.