Radiation biology of human tumour xenografts.

The radiation response of human tumour xenografts can be measured with sufficient accuracy using cell survival in vitro and tumour growth delay in vivo as endpoints. There is evidence that the radiation response of xenografts mirrors the clinical radioresponsiveness of the corresponding tumours in patients. Consequently, xenografts may have a significant potential in experimental radiotherapeutic research, e.g. in the development of in vitro and in vivo predictive assays of clinical radioresponsiveness. However, there are at least three main disadvantages with xenografts as models for human cancer. Firstly, the volume doubling time is usually shorter for xenografts than for tumours in patients. Secondly, the haematological system and the vascular network of xenografts originate from the host. Thirdly, host defence mechanisms may be active against xenografts. These disadvantages may limit the usefulness of xenografts as models for human cancer in some types of radiobiological studies.