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The treatment works by killing cancer cells and triggering the immune system to attack tumors, 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 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 tumors.
Not everyone benefited from the therapy, however. According to the study, treatment response of more than six months occurred in only about 16 percent of patients in the T-VEC group. However, that was still much better than the 2 percent response rate of those in the group that didn't receive the treatment, the researchers reported.
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 tumors -- 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.
"Because viral treatment can target cancer cells specifically, it tends to have fewer side effects than traditional chemotherapy or some of the other new immunotherapies," Harrington said in an institute news release.
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.
"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.
Two experts in the United States said the concept of viral immunotherapy does have real promise.
"The use of the genetically engineered virus in treating cancer, specifically skin cancer, will revolutionize the conventional treatment of skin cancers," predicts Dr. Michele Green, a dermatologist at Lenox Hill Hospital in New York City.
"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," she said.
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 rate of melanoma -- the deadliest form of skin cancer -- has been increasing in the United States for the past three decades. This year, the American Cancer Society estimates nearly 10,000 people will die from melanoma.
-- E.J. Mundell
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