Hyperthermia: New Hope For The Old Method Of Cancer Treatment

It is quite likely that many cancer patients did not even heard about hyperthermia therapy. Although the method is not new, its popularity as well as effectiveness is limited. But some interesting recent scientific developments may pave the way to the renaissance of this slightly ignored cancer treatment technique.

What is hyperthermia therapy and how it works?  

The term “hyperthermia therapy” refers to a type of medical treatment when the whole body or a part of body is exposed to elevated temperature for some period of time.

Although general hyperthermia was regarded as a good therapy from ancient time, its specific effect on cancer was scientifically documented only in 19^th century. It was noticed that cancer patients who experienced high fewer due to additional infectious diseases experienced a reduction of the tumor size.

What stands behind this effect?

Cancer cells are not more sensitive to the heat than normal ones. The difference originates in the disorganized vascular structure of tumors. Due to the fast growth of tumor, blood vessels within it are not properly formed. This fact has two important consequences.

• First, tumors are deprived of adequate oxygen supply (the effect known as hypoxia).
• Second, they can’t easily dissipate heat and become overheated easier than surrounding tissues.

Overheating of tumor can lead to a variety of effects. If temperature has risen too much and too fast, some proteins in the cancer cells become denatured and this causes cell death. At lower temperature, specific heat shock proteins get activated. These proteins trigger apoptosis – a programmed death of the cell. Apoptosis is a suicide program which gets activated in response to a variety of external and internal stimuli. Essentially, everything what can potentially cause severe malfunctioning of the cell (physiological stress, excessive level of damage, mutations) can lead to apoptosis. Apoptosis is a highly organized mode of cell’s self-destruction, which does not damage surrounding cells and tissues.  

Effectiveness of hyperthermia

Hyperthermia therapy, unfortunately, is simply not good enough to achieve cancer removal or reduction of its size on its own. However, the use of hyperthermia helps to enhance the effectiveness of other anti-cancer treatments. For instance, hyperthermia can increase the impact or radiotherapy and chemotherapy.

Radiotherapy alone achieves complete response only in 30% of cases. Complete response to any anticancer treatment is defined as an absence of visible signs of tumor. This doesn't mean tumor is completely eliminated – some cancer cells usually survive and can re-initiate the growth of tumor at a later stage. Nevertheless, achieving complete response significantly improve the survival rate of cancer patients.

This is up to three times higher response rate compared to the use of irradiation alone. The 5-years survival rates were 80% for patients with breast cancers, 88% for patients with head and neck cancer and 87% for patients with prostate cancer.  

Modern Advances In Hyperthermia Therapy And Cancer Stem Cells 

How is hyperthermia therapy delivered?

Overheating cancer tissues can be achieved using several methods. Microwave heating, infrared light, ultrasound can all be used. The whole body hyperthermia can be achieved simply by placing a patient in a hot room or wrapping him in hot blankets. This method aims to destroy metastatic cancer cells that already spread around the body. The whole body hyperthermia is more risky, however, and is not used often.

Blood perfusion method relies on removing the patient’s blood from the body, heating it up and returning back through the site close to tumor. The heated blood usually gets infused with chemotherapeutic drugs. This approach helps to improve the selectivity and effectiveness of anticancer drug therapy. The method is often used to treat difficult cancers in the abdominal region such as stomach cancer and peritoneal mesothelioma.  

Magnetic hyperthermia and cancer stem cells

Magnetic hyperthermia is a relatively new experimental cancer treatment.

 Most commonly used nanoparticles consist of iron oxide. They can be delivered inside tumor either by direct injection or using specialized delivery systems based on the chemical modification of nanoparticle’s surface. Once magnetic particles are inside the tumor, application of magnetic field leads to the localized generation of heat which helps to destroy cancerous cells.

New interesting phenomenon was reported recently by researchers from the University of Minnesota.

The implications of this finding can be very significant. Cancer stem cells are specialized cells that are responsible for tumor formation, progression, regrowth and spread. They are physiologically and biochemically different from the majority of tumor cells. Modern drugs can successfully eliminate the bulk of cancer cells from the body, but due to these biochemical differences they fail to target cancer stem cells. Survival of cancer stem cells ensures eventual return of cancer after chemotherapy.  

More research needed to achieve practical goals

Unfortunately, our understanding of cancer stem cells is still very poor. Even their existence is still debated by some scientists, and their definite presence is confirmed only for some types of cancer. Currently, we have no therapeutic methods of targeting and killing these cells. It is clear that without developing these methods we won’t be able to address the problem of cancer recurrence and spread. Magnetic hyperthermia might be a surprisingly effective and relatively simple method to achieve this goal. It still remains to be seen how well it will work, and more research will be needed to develop effective therapeutic approaches which are affordable and available for every patient.