Effect of hyperthermia on the hypoxic fraction in an experimental mammary carcinomain vivo

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Abstract
The influence of hyperthermia on the fraction of clonogenic hypoxic cells in a C3H mammary carcinoma [mouse] was investigated using the TCD50 [radiation dose needed to achieve 50% tumor control] values for radiation treatment under normal or clamped conditions. A 1 h heat treatment at 41.5.degree., 42.5.degree. and 43.5.degree. C given 4 h after radiation reduced the hypoxic fraction to 2.3 .times. 10-1, 7.4 .times. 10-3 and 6.5 .times. 10-3, respectively, when compared with the content of hypoxic cells in non-heated tumors. Apparently, moderate hyperthermia is able to destroy selectively a large proportion of the fraction of radioresistant hypoxic cells in a solid tumor. This effect is probably due to the increased heat sensitivity of cells in a chronically hypoxic and nutritionally deprived acidic environment.