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. Warmer temperatures can make the cells more likely to be affected by other treatments such as 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 who are experienced 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 used (or studied for use) against many types of cancer.
There are 2 very different ways in which hyperthermia can be used:
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 by coagulating the proteins in them and destroying nearby 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:
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 tip of the probe puts out a high-frequency current that creates heat (between 122° and about 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 or start to grow. It can also be added to other treatments 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 (5 cm) 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. It isn’t hot enough to destroy the cancer cells outright. It’s 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. This is done with surgery, typically with the patient under general anesthesia (in a deep sleep). 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. 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.
Another hyperthermia 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), also known as hyperthermic intraperitoneal chemotherapy (HIPEC). In studies, this has seemed helpful in treating certain types of cancer, but it isn’t yet clear if it 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.
External heating is also used for cancers that are in or just below the skin. High-energy waves are aimed at the tumor from a machine outside the body such as a microwave or ultrasound applicator. This approach is most often used with radiation treatment. During a course of radiation, hyperthermia may be used 3 out of the 5 treatment days each week. It’s typically given within the hour before the radiation is delivered.
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 heating blankets, warm-water immersion (putting the patient in warm water), or thermal chambers (much like large incubators). People getting whole body hyperthermia are sometimes given sedation (medicine to make them feel calm and sleepy) or even light anesthesia.
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 whole-body hyperthermia. Studies suggest that this may cause certain immune cells to become more active for the next few hours and raise the levels of cell-killing compounds in the blood. Some researchers take the body temperature higher, around 107° F, for short periods of time. Other studies are testing hyperthermia and chemotherapy along with other treatments that are designed to boost the person’s immune system.
Local hyperthermia, such as RFA, can destroy tumors without surgery. Scientists agree that it works best when the area being treated is kept within an exact temperature range for a precise period of time. But this isn’t always easy to do. Right now it is hard 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, even the lower temperatures used in whole body hyperthermia.
Doctors are finding better ways of 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.
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 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.
The 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 makes them easier to destroy using radiation and certain chemotherapy drugs. But careful temperature control is a must with any type of hyperthermia.
Side effects depend on what part of the body is treated and how high the temperature is raised. Whole-body and regional 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.
Isolated limb perfusion with chemotherapy can cause redness, blistering, swelling, and damage the skin and muscle. Rarely this damage can be severe enough to require that the arm or leg be amputated. Since regional and whole-body hyperthermia are often given with other cancer treatments such as chemo and radiation, side effects from these treatments may be seen then or at a later time.
Experience, improved technology, and better skills in using hyperthermia treatment have led to fewer side effects. In most cases, the problems that people have with hyperthermia are not serious.
Hyperthermia is a promising way to improve cancer treatment, but it is largely an experimental technique at this time. It requires special equipment, and a doctor and treatment team who are skilled in using it. Because of that, it’s offered in only a few cancer treatment centers in the US and Europe.
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:
Referenced from American Cancer Society (cancer.org)