Everyone is talking about the recent television reports on the use of viruses to treat cancer. The very general concept behind these treatments is that viruses can be adapted to kill cancerous cells while leaving healthy cells unaffected. This field of treatment is called Oncolytic Virotherapy. But if you've found your way to this article, you’re most likely thinking: “This is great… but what about sarcoma?”
The Sarcoma Alliance has put together this blog post as a way to provide a general overview of what oncolytic virotherapy is and how it is being studied in sarcoma. This is not a comprehensive look at all of the research that has been done pertaining to sarcoma, nor is it intended to reach conclusions about the future of oncolytic virotherapy as a sarcoma treatment. If you are interested in the studies listed below or want to learn more, we encourage you to speak with your or your loved one's treating sarcoma specialist.
While some research has been performed on sarcoma oncolytic virotherapy, there are still many challenges to developing these treatments. For example, viruses are attracted to cells with certain specific markers, so if a sarcoma cell does not have the marker for a specific virus, it won’t be attacked. Additionally, many tumor cells mutate rapidly, which can lead to markers on only some of a tumor’s cells. Conversely, if the sarcoma cells have the same type of cell markers that normal cells have, the virus might attack too many healthy cells. However, in spite of these potential complications, some preliminary studies on the efficacy of oncolytic virotherapy as a sarcoma treatment show promise.
Several types of virotherapy have been studied in sarcomas, including:
- Using viruses to directly attack the sarcoma. Since viruses kill cells, if they can be genetically “tweaked” to attack only a sarcoma, this may work well.
- Using vaccine viruses to attack the sarcoma. Vaccine viruses won’t cause disease, and since they have been used in vaccines they are known to be safe. They may kill cancer cells directly, or have the immune system attack the cells.
- Using viruses to make the immune system do a better job of attacking the sarcoma cell. In some cases, the immune system cells that attack cancer cells remain in the body only a short time, thus cancer can recur. Tying the immune response to a viral infection seems to keep these immune cells around far longer, thus preventing tumor recurrence.
- Developing drugs that attack cancer cells the same way that viruses attack cells. These drugs mimic the ways that viruses kill cells, and thus may be able to be very specific for types of cancers, as well as “recognizing” mutated tumor cells.
Published studies using viruses in a laboratory setting, both in vitro and in vivo (in these cases, mouse models), show some positive results. Below is a brief overview of some of these most recent studies:
- The measles vaccine virus has been studied and shown some promise in treating various subtypes of sarcoma.[i][ii]
- The vaccina virus (similar to cowpox, used in the vaccine for smallpox) has also been studied in advanced extremity sarcoma, which reported some positive results.[iii]
- Vesicular stomatitis virus was studied in metastatic Ewing's sarcoma mouse models, and was shown to have “selectively infected and killed EWS" and delayed tumor growth.”[iv]
Due to the nature of drug development and the potential for differing results as studies continue, it’s impossible to say whether any of these studies will lead to treatments, but we will continue to monitor these and other early developments in oncolytic virotherapies.
In addition to laboratory studies, a few clinical trials using oncolytic virotherapies for sarcoma have been completed or are underway. Below is a brief overview of some of the most recent studies:
- A handful of clinical trials of Reovirus (Reolysin) have taken place, both for pediatric and adult sarcomas.[v][vi]While previous laboratory studies showed that Reolysin may be effective therapy in sarcomas,[vii] these clinical trials had mixed results.
- A trial looking at varicella zoster virus (chicken pox) in combination with immunotherapy is currently open for osteosarcoma patients who meet certain criteria. For more information about this trial visit: https://www.clinicaltrials.gov/ct2/show/NCT01953900?term=sarcoma+virus&recr=Open&rank=8
- A Phase II clinical trial that just opened in March testing pembrolizumab in both soft tissue sarcoma and bone sarcoma patients who meet certain criteria. While not a virotherapy, Pembrolizumab (Keytruda) is a promising drug that works similarly to virotherapies, and is already approved to treat melanoma. For more information about this trial visit: https://clinicaltrials.gov/ct2/show/NCT02301039?term=pd1+and+sarcoma&rank=1