Stem Cells and Malignant Mesothelioma: An In-Depth Look

Malignant mesothelioma is a rare yet aggressive type of cancer that kills as many as 2,500 people per year in the United States alone. Most closely associated with long-term exposure to asbestos-containing material (such as insulation fibers, vinyl flooring, or auto parts), mesothelioma typically affects the lining in the lungs, heart, abdominal cavity or, in very rare cases, the testes. Mesothelioma has an extraordinarily long period of latency—meaning that people who have the disease are seldom diagnosed until many years—even decades—have passed since their initial asbestos exposure. Recently, research has shown that there is a connection between this devastating disease and stem cells—a connection worth examining more closely.

What are stem cells?

Stem cells are something people hear about every time they tune into the news—it seems each day, new scientific discoveries are being made in the realm of stem cell research. But what are they? Stem cells are a cell type present in the human body that have a unique potential: the ability to become any bodily cell type. Stem cells, then, could be viewed as the blank template upon which all other cell types can be written. They are building blocks, out of which many other cell types may be constructed.

Cancer stem cells

Cancer stem cells (sometimes referred to as “CSCs”) are a special type of stem cell found in some forms of cancer, including malignant mesothelioma. Like all stem cells, CSCs have the potential to become various other cell types. The types of cells that these CSCs have the ability to become, however, is limited in a rather grim way: they can give rise to any type of tumor-specific cell in the human body. So, just as stem cells from bone marrow have the potential to become skin cells or the cells in muscle tissue, so can CSCs become any of the cell types that a tumor is comprised of.

The role of CSCs in relapse post-treatment

Recent research findings by Swiss researchers from the Division of General Thoracic Surgery at University Hospital Berne were published in the International Journal of Oncology, and these findings suggest that CSCs may play a role in recurrence of cancer after treatment. Some tumors, thought to be completely eradicated after being treated with chemotherapy or surgery, end up coming back after treatment is completed, and researchers believe this may be due to CSCs remaining in the body even after the tumor itself has been eliminated.

The other side of the coin: systemic stem cells as a treatment option?

Although CSCs can take a remission from mesothelioma cancer and turn it upside down, there has also been research showing that certain types of treatment using stem cells could be promising. For example, a recent study by British researchers at University College London indicates that systemic treatment (a form of treatment affecting the body as a whole by being delivered via the blood steam) with stem cells programmed to cause apoptosis or death of a cell upon reaching its target may be an effective means of eradicating mesothelioma tumors. By targeting and destroying the tumor cells, the stem cells can “clear up” the cancerous cells without causing damage to the surrounding cells.

Attacking Mesothelioma Stem Cells

With the stem cell theory of cancer in mind, some researchers are working to develop new treatments for mesothelioma and other cancers that would specifically target the stem cells responsible for tumor growth. One drug that was developed to attack and kill mesothelioma stem cells made it as far as clinical trials, where new drugs are first tested on human subjects. Unfortunately the trial was halted because the drug did not seem to be working.

The drug was called defactinib and it showed promising results in phase I clinical trials, but not in phase II, which involved more participants. The patients tolerated the drug well, so safety was not an issue. The efficacy, on the other hand, proved to be low in the 372 patients involved in the trial. The results for the patients getting the drug were no better than for patients receiving a placebo. Because of the disappointing results, the trial was stopped.

Because this one drug did not work to target and kill mesothelioma stem cells does not mean that this line of research is over. More drugs are being developed and tested, and in fact, defactinib may be tested again in combination with different chemotherapy drugs.

Mesenchymal Stem Cell Treatment

Another type of stem cell treatment that is under study for targeting mesothelioma is called mesenchymal stem cell treatment. Mesenchymal stem cells are stem cells that were discovered in the stroma, which is connective tissue found throughout the body. These cells have been found to be able to differentiate into bone, cartilage, fat, and muscle cells. They also may have the ability to moderate the immune system, although exactly how they work is still not completely understood. Researchers are investigating how these stem cells could be used to treat a range of diseases.

At the Pacific Mesothelioma Center the researcher are using mesenchymal stem cells to try to develop new treatments for mesothelioma. These stem cells are being tested as vectors for delivering drugs to tumors and for use as supplements to immunotherapy treatments. Mesenchymal stem cells may be able to enhance the body’s immune system to help it target and kill cancer cells.

Implications for the future

Although the recent research findings for therapeutic usage of systemically-delivered stem cells show promise, these findings have been preliminary, and more research is needed to determine the validity and efficacy of those initial findings.

However, should further trials prove successful, stem cell therapy could be a new, safer means of treatment offering far fewer side effects and far less recovery time than traditional means of treatment, possibly with more effectiveness—thus, hopefully, leading to an increase in overall quality and length of life for patients who undergo the treatment.

Can I opt for stem cell treatment of my mesothelioma?

If you or someone you know has been diagnosed with malignant mesothelioma and would be interested in participating in research endeavors that are underway for exploring the possibilities of stem cell treatment for mesothelioma tumors, speak with an oncologist about enrolling in clinical trials.

While the treatments offered by clinical trials are limited to those trials you qualify for (and are often limited by geographic area that the research is being performed in), you may be able to participate in a trial studying the effects of stem cell treatment on mesothelioma cancer in human subjects. Speak with your physician to find out which studies you may qualify for.