What’s new in malignant mesothelioma research and treatment?

There is always research going on in the area of mesothelioma. Scientists are looking for ways to prevent, diagnose, and treat mesothelioma. Despite recent progress, much remains to be learned about the best way to treat these cancers.

Causes and prevention

Much of the research on mesothelioma has focused on learning exactly how asbestos changes mesothelial cells and their DNA to cause these cancers. Understanding how these fibers produce cancer might help us develop ways to prevent those changes.

The role of asbestos in increasing the risk of mesothelioma is a definite public health concern. Researchers are learning more about which fibers can produce cancer, how they cause these cancers, and what levels of exposure can be considered safe. Now that the dangers of asbestos are known, we can limit or stop exposure in homes, public buildings, and the workplace. Unfortunately, regulations protecting workers from asbestos exposure are much less stringent in some countries than in others.

Research is also under way to clarify the role (if any) of SV40, a virus that has been linked to mesothelioma in some studies.

Genetics

Researchers are starting to understand how certain changes in DNA can cause normal cells to become mesothelioma cells. DNA is the substance in our cells that carries the instructions for nearly everything they do.

Some genes (parts of our DNA) contain instructions for controlling when our cells grow and divide into new cells. Certain genes that cause cells to grow and divide are called oncogenes. Others that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.

Researchers have found some of the important DNA changes in mesothelioma cells in recent years. Continued research in understanding these changes may lead to new tests for earlier diagnosis and new drugs for more effective treatment.

Treatment

Mesothelioma remains a difficult cancer to treat, and doctors are constantly trying to improve on current approaches. The exact roles of surgery, radiation therapy, and chemotherapy in the treatment of mesothelioma are highly debated. Combinations of these treatments, called multimodality therapy, are now being tested and may provide the most promising option for some patients. Newer types of treatment now being studied may give patients and their doctors even more options.

Chemotherapy

Some chemotherapy drugs can shrink or slow the growth of mesotheliomas, but in most cases the effects last for a limited time. Several newer chemotherapy drugs, including raltitrexed, are now being tested in clinical trials, often together with other types of treatment.

As mentioned in the section “Chemotherapy for malignant mesothelioma,” doctors are exploring giving chemotherapy drugs directly into the chest or abdomen, often right after surgery. In some cases the drugs are heated before they are given. Doctors hope that putting the drugs directly into contact with the tumors may help them work better, while limiting the side effects in the rest of the body.

Photodynamic therapy

Another technique now being studied is photodynamic therapy (PDT). For this treatment, a light-activated drug is injected into a vein. The drug spreads throughout the body and tends to collect in cancer cells. A few days later (usually just after surgery for the mesothelioma), a special red light on the end of a tube is placed into the chest cavity. The light causes a chemical change that activates the drug and causes the cancer cells to die. Since the drug is only active in the areas exposed to the special light, this approach may cause fewer side effects than use of drugs that spread throughout all tissues of the body. Several clinical trials are now studying the use of PDT for mesothelioma.

Targeted drugs

In general, chemotherapy drugs are limited in their effectiveness against mesothelioma. As researchers have learned more about the changes in cells that cause cancer, they have been able to develop newer drugs that specifically target these changes. Targeted drugs work differently from standard chemotherapy drugs. They may sometimes work when chemotherapy drugs do not, and they often have different (and less severe) side effects.

One group of targeted drugs is known as angiogenesis inhibitors. These drugs slow the growth of new blood vessels (angiogenesis), which tumors need to grow larger. Some of these drugs are already used to treat other types of cancer and are now being studied for use against mesotheliomas. Examples of these drugs include bevacizumab (Avastin^®) and sorafenib (Nexavar^®).

Other new drugs have different targets. For example, some new drugs target mesothelin, a protein found in high levels in mesothelioma cells.

Other targeted drugs are already used to treat other types of cancer and are now being tested in mesothelioma clinical trials, including imatinib (Gleevec^®), dasatinib (Sprycel^®), bortezomib (Velcade^®), and vorinostat (Zolinza^®).

Newer forms of treatment

Because standard treatments often have limited usefulness against mesothelioma, researchers are studying other new types of treatment as well.

A newer type of treatment being tested on mesothelioma is gene therapy, which attempts to add new genes to cancer cells to make them easier to kill. One approach to gene therapy uses special viruses that have been modified in the lab. The virus is injected into the pleural space and infects the mesothelioma cells. When this infection occurs, the virus injects the desired gene into the cells. In one version of this approach, the virus carries a gene that helps turn on the immune system to attack the cancer cells. Early studies of this approach have found it may shrink or slow the growth of mesothelioma in some people, but more research is needed to confirm this.

Other new treatments called cancer vaccines are also aimed at getting the immune system to attack the cancer. In one approach, immune cells are removed from a patient’s blood and treated in the lab to get them to react to tumor cells. The immune cells are then given back to the patient as blood transfusions, where it is hoped they will cause the body’s immune system to attack the cancer. This approach is now being studied in clinical trials.