The availability of recombinant haemopoietic
growth factors has permitted more precise in vitro experiments and human in vivo studies to be performed. In general, the results have been in accord with expectations from previous in vitro studies. The clinical exploitation of the haemopoietic
growth factors offers great promise but careful studies are required to define their value. The effects of some
growth factors are multiple and complex, and it cannot be assumed that improvements in blood cell counts are per se beneficial to the patient under all circumstances. Randomized controlled trials with clinical end-points are now essential. In the situation of
chemotherapy-induced
neutropenia, large studies would be required to show an improvement in mortality although lesser morbidity would be easier to demonstrate. In the field of
cancer therapy the major benefit of the haemopoietic
growth factors will be if they permit dosage escalation and there is a consequent improvement in response rate and long-term survival. This will require careful patient selection and large, probably multicentre, trials. It is also likely that such studies will be limited by the development of severe
thrombocytopenia and an effective means to ameliorate this (perhaps the elusive
thrombopoietin) will be required. The possibility of using haemopoietic
growth factors as an adjunct to the treatment of severe
infections is enticing, but designing a trial to evaluate this possibility is fraught with difficulties. Finally, it must be noted that all the studies reported to date use single factors. This is just the beginning and the use of other factors and synergistic combinations may give greater efficacy without increased toxicity.