Hyperthermia in cancer therapy: the biological basis and unresolved questions.

This article considers the biological basis of hyperthermia in cancer therapy. More specifically, it focuses on research obser vations which suggest that hyperthermia is especially damaging to tumor tissue versus normal tissue, and it suggests new directions for research which may be useful for predicting and maximizing this difference. It is unlikely that hyperthermia alone will be useful for the permanent local control of tumors. Virtually all clinical studies (reviewed in References 41 and 57) use hyperthermia in combi nation, primarily with radiation but also with chemotherapy. Although hyperthermia interacts synergistically with radiation and some drugs when the agents are applied simultaneously, it has not been established that this synergism is greater in tumor tissue than in normal tissue. For this reason and others, hyper thermia and radiation are usually applied with a time interval of a few hours or longer between the two forms of treatment. Within this context, it is believed that each agent is preferentially effective against different cell populations within the same tumor. Research dealing with the biological effects of 41-45°C hy