Virotherapy is a new way of treating cancer. It uses a modified virus to attack cancer cells. Now, in the first positive phase 3 trial of cancer virotherapy, scientists have had success in using a modified herpes virus to attack melanoma cells. In even better news the treatment also seems to have the potential to treat cancer that has already spread to the rest of the body.

Melanoma is a very aggressive and deadly form of skin cancer. The drug that was used in this trial, T-VEC, is a modified version of the common herpes virus. It is the first time that this form of treatment has been shown to be successful in a phase 3 trial. Phase 3 is the final stage of clinical testing, so it could potentially mean that the drug could be available in the next few years, possibly even next year.

In the trial which involved 400 patients with aggressive melanoma, one in four patients responded to the treatment, with 16% still in remission after 6 months. About 10% of patients had complete remission with no detectable cancer remaining. If these patients are still cancer free after 5 years it would be considered a cure. The reason this is so exiting is that all the patients had no treatment options left as they had very aggressive melanoma which had already spread to other parts of the body, including the lungs and the liver.

The treatment works in two ways . The herpes virus used was modified to stop it from producing a protein that allows it to infect healthy cells.  However the cancer cells produce their own version of this blocked protein  allowing the virus to replicate in the cancerous tissue. The virus rapidly multiplies inside the cancer cells until they literally explode and release the virus into the surrounding tissue, which then causes a secondary immune reaction against the tumour.

Once the immune system has been primed by the T-VEC treatment it then seems to also the attack cancer at other sites where the cancer has migrated to. It is still unclear what drives this process but it is good news. The latest trial confirmed this effect, showing that secondary tumours not infected buy the virus also shrank or disappeared.

The therapy was given by injection every 2 weeks for 18 months and there were few side effects. The trial found that people with stage 3 and 4 melanoma treated with T-VEC lived an average of 41 months, compared to 21.5 months in the control group, who were given a protein designed to stimulate an immune response against the cancer, but without the virus component.

The drug has been submitted for approval and could be available as early as next year.