A promising type of cancer treatment called viral therapy avoids detection by the body's immune system and reaches tumours by 'piggybacking' on blood cells.

Hitching a ride on blood cells helps shield such experimental viral therapies from destruction by antibodies, the body's natural police force, say researchers from the University of Leeds and The Institute of Cancer Research.

The research involved a small number of patients, and did not measure effects of the treatment on patients' wellbeing or disease.

But its results suggest that viral therapies could be injected into the bloodstream in the same way as certain chemotherapy drugs.

This is preferable to injecting the virus directly into tumours - a more difficult procedure requiring technical expertise.

Several viral therapies have shown promise in clinical trials, but researchers have not yet worked out the best way to give them to patients.

Ten patients with advanced bowel cancer who were due to have surgery on tumours that had spread to the liver took part in the study. They were given up to five doses of a viral therapy called reovirus in the weeks before surgery.

Blood tests carried out shortly after treatment found the active virus had piggybacked onto blood cells. Subsequent blood samples showed that the hitch-hiking virus was quickly eradicated from the patients' blood system after completing its task.

Around four weeks after the surgery, tests on different tissues showed that the virus was active in the tumour, but not the healthy parts of the liver. This suggests that reovirus specifically targets the cancer after being injected into the bloodstream.

University of Leeds Professor Alan Melcher, part-funded by Cancer Research UK, led the study team. He said: "It seems that reovirus is even cleverer than we had thought.

"By piggybacking on blood cells, the virus is managing to hide from the body's natural immune response and reach its target intact. This could be hugely significant for the uptake of viral therapies like this in clinical practice."

The authors also say that because the virus can be injected into the bloodstream, it could be used for a wide range of cancers, rather than being restricted only to ones that need to be injected directly.

Dr Julie Sharp, senior science information manager at Cancer Research UK, said: "This promising study shows that reovirus can trick the body's defences to reach and kill cancer cells and suggests that it could be given to patients using a simple injection.

"We look forward to seeing how this research develops and if this could one day become part of standard cancer treatment."

It was published in the journal Science Translational Medicine.

Source: CRUK