Fig. 4. Schematic diagram to illustrate how accelerating repopulation of tumours (that may occur with improving nutrition) can overcome the killing effects of repeated doses of drugs or radiation.

It is assumed that 70% of tumour cells are killed after each administration of chemotherapy, which is given at 3-week intervals. a Assumes a constant rate of repopulation of surviving tumour cells between treatments, characterised by a doubling time of either 10 days or 2 months. b Assumes accelerating repopulation of surviving tumour cells between successive courses of chemotherapy, characterised by the indicated doubling times. c Assumes a delay in onset of repopulation after each cycle of chemotherapy, followed by accelerating repopulation of surviving tumour cells with the indicated doubling times. Note that accelerated repopulation can lead to the remission and regrowth of tumours during chemotherapy, as is commonly observed in clinical practice, without any change in the intrinsic chemosensitivity of the tumour cells. TD cell doubling time. Adapted from Kim and Tannock [22].