Recent clinical trials found that a modified version of the herpesvirus, along with the immunotherapy drug nivolumab, successfully shrank tumors in one-third of patients with deadly melanoma whose cancer had stropped responding to medication.

According to Everyday Health, skin cancer is the most common type of cancer in the U.S. and melanoma, although rare, causes a large majority of skin cancer deaths. Immunotherapy treatments that use the body's own immune system to fight cancer have reduced the number of melanoma deaths over the past decade, but not everyone responds to the treatment.

Oncologist Dr. Gino In, co-author of the current study being conducted at the Keck School of Medicine at the University of Southern California, said that about half of people with this form of advanced cancer run out of treatment options.

The new therapy developed by In and his colleagues uses a virus known as RP1, a genetically modified version of herpesvirus. Unlike the traditional virus, RP1 is engineered to selectively infect and destroy cancer cells while sparing healthy tissue. Once injected directly into melanoma tumors, RP1 not only causes cancer cells to burst but also releases signals that wake up the immune system, making it more active and more likely to attack cancer throughout the body. When combined with nivolumab — a checkpoint inhibitor that removes the "brakes" on immune cells — this duo demonstrated promising synergy.

Researchers enrolled 140 study participants whose advanced melanoma continued to grow despite current immunotherapy treatments. They injected RP1 into the tumors every two weeks for up to eight doses, along with intravenous nivolumab. The drug combo shrank not only the injected tumors by 30% in 1 out of 3 participants but also shrank tumors that weren't injected indicating that the treatment targets cancer throughout the whole body. The hope is that treatments like RP1 may provide a lifeline for patients whose disease no longer responds to standard therapies, marking a new chapter in the fight against advanced melanoma.

"That expands the potential effectiveness of the drug because some tumors may be more difficult or impossible to reach," said In. The side effects were mild, mimicking cold-like symptoms. A phase 3 trial has begun and the combination therapy is currently under priority review by the Food and Drug Administration.