What’s New in Rhabdomyosarcoma Research?

The treatment of rhabdomyosarcoma (RMS) has come a long way in the past few decades, and more patients are surviving RMS than ever before. However, more work needs to be done. Research on RMS is being done at many medical centers, university hospitals, and other institutions across the world.

Better classification of rhabdomyosarcomas

Newer molecular techniques are helping doctors better categorize RMS and predict which patients will respond best to certain treatments. For example, rather than just looking at the cancer cells under a microscope, researchers have begun to use special genetic tests to help classify RMS.

About 1 out of 4 cancers that doctors would usually classify as alveolar rhabdomyosarcoma (ARMS) have been found to lack the typical gene change (the PAX/FOXO1 fusion gene) seen in ARMS. These cancers have been found to act more like embryonal rhabdomyosarcoma (ERMS), which generally needs less intensive treatment than ARMS. Because of this finding, doctors can now give patients with these cancers less intense treatments and still achieve the same results.

Improving standard treatments

A major goal of current research is to treat all patients more effectively, while reducing the need for intensive treatments (and their side effects) when possible. For example, researchers are studying whether children who have a low risk of the tumor recurring can be treated without using potentially harmful treatments such as radiation therapy.

Because children’s bodies are very sensitive to radiation, doctors are looking for ways to limit the doses as much as possible. Newer radiation therapy techniques allow doctors to aim the radiation more precisely, limiting the amount that reaches normal body tissues. Some of these techniques are described in Radiation Therapy for Rhabdomyosarcoma.

Other ways to give radiation are also being studied. For example, in stereotactic body radiation therapy (SBRT), a special machine aims very thin beams of radiation at the tumor from many different angles, concentrating it on the tumor very precisely for short periods of time.

Proton beam radiation is another newer approach. Standard radiation beams give off the same amount of radiation at all points as they pass through the body. Proton beam radiation uses radioactive particles that travel only a certain distance before releasing most of their energy. Doctors can use this property to limit the radiation reaching normal body tissues. This approach seems promising, but it’s not yet clear if it’s better than other newer forms of radiation therapy. It’s also available in only a limited number of centers around the country at this time.

Doctors are also studying adding newer chemotherapy drugs such as irinotecan and temozolomide to the standard chemotherapy regimens for patients who have a higher risk of the tumor recurring.

For patients at a high risk of tumor recurrence, doctors have looked at giving chemotherapy more frequently (such as giving it every 2 weeks instead of every 3 weeks). This concept is called interval compression. But so far, it's not clear whether this works better than giving it at standard intervals.

Newer targeted drugs and immunotherapy

Drugs that target specific parts of cancer cells (as opposed to just attacking fast-growing cells, as chemotherapy drugs do) are now being studied for use in RMS. Some of these drugs are already being used to treat certain adult cancers. Examples of newer targeted drugs being studied for use against RMS include:

• IGF-1R inhibitors, such as cixutumumab (IMC-1A2) and ganitumab (AMG479)
• Drugs that affect a tumor’s ability to make new blood vessels, such as bevacizumab (Avastin), sorafenib (Nexavar), and regorafenib (Stivarga)
• Drugs that target the mTOR protein, such as temsirolimus (Torisel) and everolimus (Afinitor)
• Drugs that target the ALK protein, such as crizotinib (Xalkori)
• Drugs that target the cell’s hedgehog pathway, such as sonidegib (Odomzo)
• Drugs that target other cellular proteins, such as dasatinib (Sprycel)

Researchers are also testing ways of boosting the body's own immune system to treat RMS. For example, some researchers are looking at exposing some of the body’s immune system cells, called dendritic cells, to the abnormal PAX-FOXO1 protein that is found in many ARMS cells. The hope is that the dendritic cells will then cause the immune system to attack these cells, no matter where they are in the body.

Eventually, a combination of these approaches may prove to be the best way to treat RMS.