The researchers found that 16.3% of melanoma patients who received T-VEC had a strong treatment response lasting more than 6 months, compared with only 2.1% of patients who received the control immunotherapy.
The trial was led by researchers from The Institute of Cancer Research (ICR) and the Royal Marsden NHS Foundation Trust - both in the UK - and published in the Journal of Clinical Oncology.
In the US, rates of melanoma have been on the rise for the past 3 decades. This year, around 73,870 new cases of melanoma will be diagnosed, and almost 10,000 people will die from the disease.
According to the research team - led by Kevin Harrington, professor of biological cancer therapies at ICR and honorary consultant at the Royal Marsden - their study represents the first phase 3 trial to demonstrate the benefits of viral immunotherapy for cancer patients.
Herpes virus engineered to produce immune-boosting molecule
To reach their findings, Prof. Harrington and colleagues randomized 436 patients with advanced, inoperable malignant melanoma to receive either an injection with T-VEC or a control immunotherapy.
Developed by biopharmaceutical company Amgen - who funded the study - T-VEC is a genetically modified form of the herpes simplex virus type 1 (HSV-1), which can multiply inside cancer cells and kill them.
The virus has been engineered to produce a molecule called GM-CSF, which works by coaxing the immune system to destroy cancer cells. The virus has also been modified to remove two genes - ICP34.5 and ICP47 - preventing it from multiplying in healthy cells.
"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 marshaling the immune system against them," explains Prof. Harrington.
"And because viral treatment can target cancer cells specifically," he adds, "it tends to have fewer side effects than traditional chemotherapy or some of the other new immunotherapies."
Treatment response lasted longer than 3 years for some patients given T-VEC
Compared with patients who received the control immunotherapy, those who received T-VEC showed a much better treatment response.
The researchers found that 16.3% of patients who received T-VEC had a strong treatment response lasting more than 6 months, compared with only 2.1% of patients who received the control immunotherapy.
The treatment response of some patients given T-VEC even lasted longer than 3 years - a time period oncologists frequently use as a benchmark for a cure when it comes to cancer immunotherapy, according to the team.
Patients with stage III and early stage IV melanoma who were given the control immunotherapy survived for an average of 21.5 months, the results show, while those who received T-VEC lived for an average of 41 months.
The researchers found patients with stage IIIB, IIIC and IVM1a melanoma - less advanced forms of the cancer - showed the strongest responses to T-VEC, as did those who had not undergone any other treatment for the disease. This indicates that T-VEC could be used as a primary treatment for inoperable metastatic melanoma, notes the team.
"It is encouraging that the treatment had such a clear benefit for patients with less advanced cancers," says Prof. Harrington. "Ongoing studies are evaluating if it can become a first-line treatment for more aggressive melanomas and advanced disease."
Prof. Paul Workman, chief executive of ICR, believes the findings emphasize the benefits for using human viruses to tackle cancer:
"We may normally think of viruses as the enemies of mankind, but it's their very ability to specifically infect and kill human cells that can make them such promising cancer treatments.
In this case we are harnessing the ability of an engineered virus to kill cancer cells and stimulate an immune response. It's exciting to see the potential of viral treatment realized in a phase 3 trial, and there is hope that therapies like this could be even more effective when combined with targeted cancer drugs to achieve long-term control and cure."
Last month, Medical News Today reported on study by researchers from the Washington University School of Medicine in St. Louis, MO, which revealed how personalized vaccines can trigger a strong immune response against tumor mutations in patients with melanoma.