Effect of hyperthermia on hypoxic cell fraction in tumor

The effect of hyperthermia on the proportion of hypoxic cells in SCK mammary tumor of A/J mice was investigated. About 45% of clonogenic cells in the unheated control tumor were radiobiologically hypoxic. Upon heating with a 43.5 degree C water bath for 30 min, the proportion of hypoxic cells increased and then decreased: it was 95% at 5 hr and 60% at 12 and 24 hr after heating. Despite the increase in the proportion of hypoxic cells 5 hr after heating, the absolute number of hypoxic cells in the tumors at this time was significantly smaller than that in the unheated control tumors because of a decrease in the total number of surviving tumor cells. The initial increase in the proportion of hypoxic cells after heating may be attributed mainly to vascular occlusion. Proliferation of cells in the oxic area, and thus an increase in oxic cell number, appears to account for the decline in the proportion of hypoxic cells from 5 hr after heating.