We now know that some viruses do indeed go after cancerous cells in the body, with occasionally surprising effectiveness. Cancer cells possess a few traits that viruses tend to like, including rapid reproduction and a high level of metabolic activity, Rabkin says. This can make a tumor cell an ideal home for a virus, until the virus destroys it and moves on to another cell... In 2013, a Minnesota woman named Stacy Erholtz received an experimental treatment for her multiple myeloma, a cancer of the blood plasma cells. Doctors injected a massive dose of an attenuated measles virus into her body. The genetically modified pathogen homed in on tumors, killing cancer cells and kickstarting a process that recruited her immune system to finish the job. Her cancer eventually went into complete remission, a startling success for an oncolytic virus, says Russell, who helped develop her treatment. It’s likely that cases like Erholtz’s, in which the patient is successfully treated with just an oncolytic virus and nothing else, are outliers. But in the last decade, researchers have begun using viruses in combination with other drugs to effectively treat cancer in a wider range of patients. The combination that saved Nielsen’s life — an oncolytic virus and an immunotherapy drug — may soon be a viable treatment for multiple forms of cancer. Dozens of clinical trials are currently testing oncolytic therapies for cancer; recent years have seen a wave of interest in the field, with big pharmaceutical companies investing in or acquiring biotech start-ups. While T-VEC is the only oncolytic cancer drug in the U.S. so far, more will likely follow.