TUMOR OXYGENATION IS INCREASED BY HYPERTHERMIA AT MILD TEMPERATURES

The effects of hyperthermia on the oxygenation status in R3230 AC tumo urs of Fischer rats were measured using a polarographic oxygen electro de system. The median pO(2) in about 10 mm diameter tumours grown s.c. in the leg of rats was 3.7 +/- 0.3 mm Hg and it significantly increas ed upon heating at modest temperatures. For example, the tumour pO(2) measured within 10-15 min after heating for 30 min at 42.5 degrees C w as about three-fold greater than that in the control tumours. About 62 % of pO(2) values measured in control tumours were < 5 mm Hg. After he ating at 42.5 degrees C for 30 min, 37% of pO(2) values were < 5 mm Hg . Such an increase in tumour oxygenation or reoxygenation of hypoxic c ells appeared to result from an increase in tumour blood flow caused b y the mild temperature hyperthermia. The presence of hypoxic cells in tumours is believed to be a major factor in limiting the effectiveness of radiotherapy, certain chemotherapy drugs and phototherapy. Hyperth ermia at mild temperatures easily achievable with the use of presently available clinical hyperthermia devices may be an effective means to overcome the hypoxic protection in the treatment of human tumours.