The Change in Hypoxic and Chronically Hypoxic Cell Fraction in Murine Tumors Treated with Hyperthermia

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Abstract
The effect of hyperthermia on the size of hypoxic and chronically hypoxic cell fractions in murine tumors was studied. The chronically hypoxic cell fraction was defined as a fraction of tumor cells which were not oxygenated under hyperbaric O2. Animals were C3Hf/Sed mice derived from a defined flora mouse colony. Tumors were FSa-II and MCa, which were early generation isotransplants of a spontaneous fibrosarcoma and a mammary carcinoma, respectively. TCD50 (50% tumor control dose), or the radiation dose which yields a local tumor control in 1/2 the treated animals, and TG (tumor growth) time, or the time required for 1/2 the treated tumors to reach 1000 mm3 from the 1st treatment day, were experimental end points. Hyperthermia was given by immersing animal feet into a water bath maintained at 43.5 .+-. 0.1.degree. C. Animal tumors were irradiated with a 137Cs unit under hypoxic conditions, in air or under O2 30 psi. The hypoxic cell fraction increased immediately after hyperthermia in both MCa and FSa-II tumors. The chronically hypoxic cell fraction was decreased following hyperthermia. The decrease was more substantial in the MCa than in FSa-II tumors.