Production of metastases by a primary tumour irradiated under aerobic and anaerobic conditions in vivo.

The effect of local irradiation of a rapidly metastasizing sarcoma in the leg of the rat was measured in terms of (a) regression of the primary tumour and (b) growth of metastases produced in lymph nodes and lungs, by dissemination occurring after irradiation of the primary tumour. These effects on rats which had been irradiated while breathing air were compared with rats breathing 10% O(2)/90% N(2) in which a tourniquet had been applied proximal to the tumour to arrest blood flow during irradiation. Tourniquet anoxia increased radioresistance of growth of primary tumour by (OER) factors of 2·9-3·3. Corresponding factors for inhibition of growth of metastases in abdominal lymph nodes, and for the reduction in incidence of lung metastases produced by single tumour cells, were 2·7 and 2·4 respectively. These results suggest that this tumour was radiobiologically well oxygenated when it was irradiated in a poorly vascularized stage of growth where tumour necrosis had developed.