A team at the University of Leeds in England found the virus, called a reovirus, inside patients' tumour cells but not in their healthy tissues.
Before the study, it wasn't clear whether the common gastrointestinal and respiratory virus could survive within the body to reach tumours. There were fears that they would not work if the immune system could wipe them out.
However, new study published in Science Translational Medicine showed the virus hides from the immune system and travels inside white blood cells to reach their target.
The findings suggest a cancer treatment based on the virus could be delivered intravenously, LiveScience reported.
While the virus could be directly injected at the site of the tumour, such injections are more complicated to administer, and difficult to use for cancers deep in the body, such as liver and pancreatic cancer, the researchers said.
In the new study, a team led by Alan Arthur Melcher injected reovirus into the bloodstreams of 10 patients who had colon cancer that had spread to the liver. A week to a month after the injections, the patients underwent surgery to remove their liver tumours.
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The team found reovirus RNA in the patients' blood plasma, the fluid that surrounds blood cells and as expected the virus there had been inactivated by the patients' immune systems.
However, the researchers found "live" viruses, still capable of replicating, inside white blood cells. In addition, samples taken during surgery showed active viruses in the liver tumour cells but not in normal liver tissue.
They also found a link between the presence of the virus and degradation of tumour cells, but they cautioned they cannot be sure the viruses caused the tumour cell destruction.
Reovirus is just one of several viruses being studied for their potential to kill cancer cells. So far, such "oncolytic virus" therapies have appeared safe, and some have advanced through early clinical trials.
The new study "is an important next step in advancing [oncolytic virus] therapies into cancer patients," said John Bell of Ottawa Hospital Research Institute.