DEAR MAYO CLINIC: I've read that someday it may be possible for doctors to use viruses to cure cancer. How does it work? What types of cancer could it affect?
ANSWER: A considerable amount of research is currently underway that's examining the use of viruses to fight cancer. It is an exciting field of study that could have an impact on the treatment of many forms of cancer. Recent clinical trials of virus therapy for one type of blood cancer, multiple myeloma, have been particularly successful.
In the multiple myeloma study, a measles virus was used to target the cancer cells. The specific form of the virus is actually a strain of the measles vaccine that was developed in the 1950s. Laboratory research has shown it to be quite effective in infecting and killing cancer cells. But because it is a vaccine strain, it is not able to damage healthy body tissues.
For the clinical trial, the researchers modified the virus so it could be easily seen on imaging studies, such as a nuclear medicine scan. To do this, they included in the virus a gene naturally present in the thyroid gland. One of the tasks of the thyroid gland is to remove iodine from the blood. So when the thyroid gene is in the virus, the location of the virus can be tracked in the body using an iodine scan.
In the future, the thyroid gene in the virus may be used to absorb a potent form of radioactive iodine treatment to enhance the power of the measles virus against cancer. But for now, it's only a tracking tool.
Multiple myeloma was chosen for the study in part because it can be a challenging cancer to effectively treat. It often appears throughout the bone marrow and in the following bones: skull, ribs, limb bones, spine and pelvis. Results showed that high doses of the modified measles vaccine virus did have an impact. In one patient in particular who had several tumors, as well as cancer in her bone marrow, the virus treatment appeared to effectively attack and destroy the cancer cells without significant side effects.
With those results in mind, research will continue to the next phase of clinical trials. The focus for those trials will remain multiple myeloma. But other kinds of cancer are being studied to see if oncolytic viruses could be an effective treatment for them, as well. They include ovarian cancer, head and neck cancer, mesothelioma and brain cancer. Development of a variety of other oncolytic viruses is ongoing, as well.
The hope is that eventually these viruses will be able to provide long-term control of cancer with just one dose. That is very different from today's existing cancer therapies, such as chemotherapy or radiation therapy, that must be given repeatedly and can be associated with some severe side effects. Although a significant amount of research remains before viruses can be used as standard cancer treatment, the future for this therapy looks promising. -- Stephen Russell, M.D., Ph.D., Molecular Medicine, Mayo Clinic, Rochester, Minn.
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