ARCON--current status: summary of a workshop on preclinical and clinical studies.

The current status of the experimental and clinical studies of ARCON was presented. This is a new approach aimed at increasing the effectiveness of radiotherapy by acceleration in order to avoid tumour cell regeneration during therapy and using two forms of radiosensitizer of hypoxic cells. The background knowledge about human tumour proliferation and oxygenation was expertly reviewed. New experimental data were presented for various aspects of carbogen, Nicotinamide and a range of other potential sensitizers. These included mechanistic investigations, radiobiological studies of clinically relevant dose levels, tumour and normal tissue effects, pharmacology and blood flow measurements. Clinical data for both toxicity and initial estimates of the tumour response were presented. Extensive discussions about the side effects of Nicotinamide took place. The main conclusions from the preliminary clinical results were encouraging, especially in head and neck and bladder tumours. Two studies showed that local control is considerably increased compared with previous experience and with results from centres of excellence elsewhere. Several other clinicians reported optimism. So far, ARCON has not been taken into randomized clinical trials and the data are therefore still, of necessity, compared with historical controls or with general clinical experience.