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Description of hyperthermia
In oncology, the generation of a higher temperature at a tumor-involved region of the body is called hyperthermia. There is a variety of temperature ranges going from 39 – 40 °C up to such high temperatures as 80 – 90 °C, and accordingly a number of techniques to induce those temperatures under well-controlled conditions.
Temperature is a highly conserved and important parameter in all living systems. In mammalians, particularly in humans, a narrow range of 37.0 – 37.5 °C is attempted to be maintained by regulation. In this range, the complicated cellular and physiological processes are working most efficiently. Under stress conditions, e.g. infectious diseases, fever is a reaction of the organism to better handle with the external attacks.
During the past along the milleniums, physicians have repeatedly tried to utilize artificial temperature elevations for the treatment of various kinds of diseases, e.g. by induction of fever. Also for tumor diseases, in anecdotal cases a beneficial effect was found. Because of the complexity of interactions, the attempts were often too unspecific to be really successful.
Since research in molecular biology is continuously growing, we recognize that a large number of intracellular processes exist with a specific temperature-dependent behaviour. There have been found various interactions in the laboratory which have a large potential to be helpful in cancer treatment.
Among these mechanisms there is evidence of
- Enhancement of anti-tumor effects of various drugs (also cytostatics) and radiation (typically in the range 40 – 43 °C)
- Induction of immunological processes (39 – 41 °C, fever range)
- Induction of gene expression and protein synthesis (40 – 42 °C)
- Influencing the tumor microenvironment in a way that makes the tumor better accessible for some therapies
Of course, there is always a cytotoxic effect of heat by itself, typically at higher temperatures (above 43 °C). This effect is mainly exploited in thermoablative interventions.
However, the most beneficial contribution of hyperthermia for oncological treatments will be based on enhancing the effectiveness of other treatment modalities (radiotherapy, chemotherapy, radiochemotherapy, gene therapy, immune therapy etc). The use of hyperthermia as a dose response modifying agent is in particular increasing the therapeutic ratio, i.e. enhanced effectiveness without additional toxicity.