Minors Tanning Bill

Katie Donnar shows the scar from where melanoma was on the calf of her leg, in front of a tanning bed like the one she once used. Some patients with aggressive, inoperable melanoma who received an experimental injection of a viral therapy showed a better treatment response than those who who received a control immunotherapy. (Daniel R. Patmore/Associated Press)

A genetically engineered and harmless form of the herpes virus is showing some promise in slowing the progression of melanoma, researchers report.

The treatment works by killing cancer cells and triggering the immune system to attack tumours, researchers said. The study, published May 26 in the Journal of Clinical Oncology, was funded by drug maker Amgen, which is developing the therapy.

The researchers said their study of 436 patients worldwide is the first phase 3 clinical trial to show that so-called "viral immunotherapy" — using a harmless virus to spur an immune response against cancer — can benefit cancer patients.

A phase 3 trial, typically the last and largest, is undertaken after earlier research indicates a treatment is already safe and effective in a small group.

The patients in this trial had aggressive, inoperable melanoma. Each received either an injection of the viral therapy — called Talimogene Laherparepvec (T-VEC) — or a "control" immunotherapy.

T-VEC is a modified form of herpes simplex virus type-1 or cold sore virus that has had two of its genes removed so that it can't replicate in healthy cells, the research team explained. Instead, T-VEC multiplies inside cancer cells and bursts them from within. It also produces a molecule that stimulates the immune system to attack and destroy tumours.

Not everyone benefited from the therapy, however. According to the study, treatment response of more than six months occurred in only about 16 per cent of patients in the T-VEC group. In comparison, there was a 2 per cent response rate of those in the group that didn't receive the treatment, the researchers reported.

2-pronged attack on tumours

Also, some patients in the T-VEC group had a response lasting longer than three years, the researchers noted.

"There is increasing excitement over the use of viral treatments like T-VEC for cancer, because they can launch a two-pronged attack on tumours — both killing cancer cells directly and marshalling the immune system against them," said Kevin Harrington, U.K. trial leader and professor of biological cancer therapies at the Institute of Cancer Research in London.

Responses to T-VEC were strongest in patients with less advanced cancers and in those who had not received any prior treatment, Harrington said. This highlights the potential benefits of T-VEC as a first-line treatment for patients with advanced melanoma that cannot be surgically removed, the researchers said.

Average survival among patients with stage 3 and early stage 4 melanoma was 41 months for those who received T-VEC, and about 22 months for those in the control group.

The most common side-effects with the drug were fatigue, chills, and fever. The only serious adverse event occurring in 2 per cent or more of those given T-VEC was cellulitis, a bacterial skin infection, the researchers said.

"It is encouraging that the treatment had such a clear benefit for patients with less advanced cancers — ongoing studies are evaluating if it can become a first-line treatment for more aggressive melanomas and advanced disease," Harrington added in a release.

Two experts in the United States said the concept of viral immunotherapy does have promise.

"In the future, more aggressive and complicated skin cancers such as malignant melanoma will be able to be treated through viral immunotherapy and may halt or cure the disease entirely," said Dr. Michele Green, a dermatologist at Lenox Hill Hospital in New York City.

Dr. Philip Friedlander is assistant professor of dermatology at the Icahn School of Medicine at Mount Sinai, in New York City. He believes that "T-VEC represents a significant advance and is actively being studied in combination with other immune therapies."

The Canadian Cancer Society estimates there will be 6,800 new cases of melanoma and 1,150 deaths from the disease in the country this year.

With files from CBC News