What is the importance of anaemia in radiotherapy? The value of animal studies.

It has been recognised for many years that anaemic cancer patients have a particularly poor prognosis (see recent reviews [4,8]). New data is regularly appearing in the literature, extending our knowledge to include many tumor sites. The evidence is now overwhelming that for most of these, local tumor control by radiotherapy is compromised in patients who are anaemic before and during radiotherapy. The role of the radiobiologist must be to offer an explanation for the clinical observations and to suggest a means of compensating for the problem in those patients whose treatment is prejudiced by anaemia. This statement assumes a cause and effect relationship between anaemia and tumor curability, supposedly through an impairment of oxygen transport to the tumor cells. We must then consider the consequences of a reduction in circulating haemoglobin levels in model tumor systems in animals, combine that information with our knowledge of physiological mechanisms and attempt to reconcile our conclusions with the clinical findings. We should be aware of course, that a failure to achieve this could be the result of inadequacies of the mouse model or because anaemia is simply not the cause of clinical radioresistance but rather a consequence, along with radiosensitivity of particular tumor characteristics. What do the experimental animal data reveal? We will consider two clinically important questions: 1) Are tumors in mice with lower than normal haemoglobin levels more resistant to radiation and what is the temporal relationship between duration of anaemia and sensitivity? 2) Does the restoration of haemoglobin levels before radiotherapy change sensitivity?