Hyperthermia means a body temperature that is higher than normal. High body temperatures are often caused by illnesses, such as fever or heat stroke. But hyperthermia can also refer to heat treatment – the carefully controlled use of heat for medical purposes. Here, we will focus on how heat is used to treat cancer.
When cells in the body are exposed to higher than normal temperatures, changes take place inside the cells. These changes can make the cells more likely to be affected by radiation therapy or chemotherapy. Very high temperatures can kill cancer cells outright, but they also can injure or kill normal cells and tissues. This is why hyperthermia must be carefully controlled and should be done by doctors with experience in using it.
The idea of using heat to treat cancer has been around for some time, but early attempts had mixed results. For instance, it was hard to maintain the right temperature in the right area while limiting the effects on other parts of the body. But today, newer tools allow better control and more precise delivery of heat, and hyperthermia is being studied for use against many types of cancer.
How can hyperthermia be used to treat cancer?
There are 2 main ways in which hyperthermia can be used:
- Very high temperatures can be used to destroy a small area of cells, such as a tumor. This is often called local hyperthermia or thermal ablation.
- The temperature of a part of the body (or even the whole body) can be raised to a higher than normal level. It isn’t hot enough to kill the cells directly, but this can allow other types of cancer treatments such as radiation therapy, immunotherapy, or chemotherapy to work better. This is known as regional hyperthermia or whole-body hyperthermia.
Local hyperthermia (or thermal ablation) is used to heat a small area like a tumor. Very high temperatures are used to kill the cancer cells, coagulate the proteins, and destroy the blood vessels. In effect, this cooks the area that is exposed to the heat. Radio waves, microwaves, ultrasound waves, and other forms of energy can be used to heat the area. When ultrasound is used, the technique is called high intensity focused ultrasound, or HIFU.
The heat may be applied using different methods:
- External: High energy waves are aimed at a tumor near the body surface from a machine outside the body.
- Internal: A thin needle or probe is put right into the tumor. The tip of the probe releases energy, which heats the tissue around it.
Radiofrequency ablation (RFA) is probably the most commonly used type of local hyperthermia. It uses high-energy radio waves for treatment. A thin, needle-like probe is put into the tumor for a short time, usually about 10 to 30 minutes. Placement of the probe is guided using ultrasound, MRI, or CT scans. The probe puts out a high-frequency current that creates heat (between 122° and 212°F) and destroys the cells within a certain area. The dead cells are not removed, but become scar tissue and shrink over time.
RFA is most often used to treat tumors that cannot be removed with surgery or for patients who are not able to go through the stresses of surgery. It can usually be done as an outpatient. RFA may be repeated for tumors that come back, start to grow, or to give complete treatments. It can also be added to any other treatment, like surgery, radiation therapy, chemotherapy, hepatic arterial infusion therapy, alcohol ablation, or chemoembolization.
RFA can be used to treat tumors up to about 2 inches (5cm) across. It is most commonly used to treat tumors in the liver, kidneys, and lungs, and is being studied for use in other areas of the body. Long-term outcomes after RFA treatment are not yet known, but early results are encouraging.
In regional hyperthermia a part of the body, such as an organ, limb, or body cavity (a hollow space within the body) is heated. The heat is usually combined with chemotherapy or radiation therapy.
In one approach, called regional perfusion or isolation perfusion, the blood supply to a part of the body is isolated from the rest of the circulation. The blood in that part of the body is pumped into a heating device and then pumped back into the area to heat it. Chemotherapy can be pumped in at the same time. To do this, surgery is needed to change the normal blood flow in the part of the body that is treated. Isolation perfusion is often is done under general anesthesia (drugs are used to make the patient sleep while it’s done). Depending on the body part and how long the treatment will last, the temperature used may range from 104° F to 113° F. This technique is being studied as treatment for certain cancers in the arms or legs, such as sarcomas and melanomas.
A related technique can be used along with surgery to treat cancers in the peritoneum (the space in the body that contains the intestines and other digestive organs). During surgery, heated chemotherapy drugs are circulated through the peritoneal cavity. This is called continuous hyperthermic peritoneal perfusion (CHPP) or hyperthermic intraperitoneal chemotherapy (HIPEC). In studies, this has seemed helpful in treating certain types of cancer, but it isn’t yet clear if this treatment is better than other types of treatments.
Another approach to regional hyperthermia is deep tissue hyperthermia. This treatment uses devices that are placed on the surface of the organ or body cavity and produce high energy waves directed at a certain area. These devices give off radiofrequency or microwave energy to heat the area being treated.
Whole-body heating is being studied as a way to make chemotherapy work better in treating cancer that has spread (metastatic cancer). Body temperature can be raised by using warm-water blankets, warm-water immersion (putting the patient in warm water), inductive coils (like those in electric blankets), or thermal chambers (much like large incubators). The body temperature may be raised to about the level a person would have if they had a fever, which is sometimes called fever-range hyperthermia. A few studies take the body temperature higher, around 107° F, for short periods of time. At least one human study suggests that this may cause certain immune cells to become more active for the next few hours. Other studies are testing hyperthermia and chemotherapy along with other treatments that are designed to boost the activity of the person’s immune system. (See our document called Immunotherapy for more information.)
Pros and cons of hyperthermia
A major advantage of regional and whole body hyperthermia is that they seem to make other forms of cancer treatment work better. Heating cancer cells to temperatures above normal (up to as high as 113° F) makes them easier to destroy using radiation and certain chemotherapy drugs. And local hyperthermia, such as RFA, can use very high temperatures to destroy tumors without surgery.
Careful temperature control is a must. Scientists agree that hyperthermia works best when the area being treated is kept within an exact temperature range for a certain period of time. But this isn’t always easy to do. Right now there is no way to accurately measure the temperature inside a tumor. And keeping an area at a constant temperature without affecting nearby tissues can be tricky, too. To add to this, not all body tissues respond the same way to heat – some are more sensitive than others. For example, the brain is very sensitive to heat.
Another problem is monitoring the temperature at the site being treated. Small thermometers on the ends of probes can be placed in the treatment areas to be sure the temperature stays within the desired range. Magnetic resonance imaging (MRI) is a newer way that temperature can be monitored without putting in probes, and this has become the preferred method for most.
The possible side effects of hyperthermia depend on the technique being used and the part of the body being treated. Most side effects are short-term, but some can be serious.
Local or regional hyperthermia can cause pain at the site, infection, bleeding, blood clots, swelling, burns, blistering, and damage to the skin, muscles, and nerves near the treated area.
Whole-body hyperthermia can cause nausea, vomiting, and diarrhea. More serious, though rare, side effects can include problems with the heart, blood vessels, and other major organs.
Experience, improved technology, and better skills in using hyperthermia treatment have led to fewer side effects. In most cases, the problems that people do have are not serious.
The future of hyperthermia
Hyperthermia is a promising way to improve cancer treatment, but it is largely an experimental technique at this time and is not commonly used. Many clinical trials of hyperthermia are being done to better understand and improve this technique. For instance, the use of nanoparticles and the induction heating of magnetic materials that are implanted into tumors are some new types of hyperthermia that are under study. And researchers continue to look at how hyperthermia is best used along with other cancer treatments to improve outcomes.
Studies are also looking at ways to reach deeper organs and other sites that cannot be treated with hyperthermia at this time. Current studies are looking at how it might work to treat many types of cancer, including the following:
- Colorectal (with spread to liver)
- Head and neck
- Sarcomas (soft tissue cancers)
For more information about clinical trials of hyperthermia, contact the National Cancer Institute (NCI) at 1-800-4-CANCER (1-800-422-6237) or visit the NCI Web site at www.cancer.gov/clinicaltrials.
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Last Revised: 08/30/2011