Leaving healthy tissue alone, the virus spreads through the bloodstream and infects tumour cells anywhere in the body.
The trial during which the virus was delivered by intravenous injection saw tumours, including the fatal mesothelioma, shrink or stop growing in six out of eight patients on the highest dose.
"Using a virus to treat cancer certainly sounds groundbreaking. In cases where patients are suffering from mesothelioma which is extremely difficult to treat and so far impossible to cure, it could provide renewed hope for future treatments," said Emma Costin of Simpson Millar.
Professor John Bell of The Ottawa Hospital Research Institute said: "We are very excited because this is the first time in medical history that a viral therapy has been shown to consistently and selectively replicate in cancer tissue."
The JX-594 virus, which has been engineered to have anti-cancer properties, stems from a strain of the smallpox vaccine.
The trial was carried out on 23 patients with advance cancers that were not responding to traditional treatments. Aside from a few flu-like side effects, the virus infusion caused no major discomforts.
"This new study is important because it shows that a virus previously used safely to vaccinate against smallpox can now be modified to reach cancers through the bloodstream - even after cancer has spread widely through the patient's body," said Professor Nick Lemoine, of Cancer Research UK and
added: "It is particularly encouraging that responses were seen even in tumours such as mesothelioma, a cancer which can be particularly hard to treat."
Further studies are now expected to take place.