07/12/2025
Great news.
Scientists have cleverly repurposed the herpes virus, turning what’s usually seen as a pesky infection into a cancer-fighting weapon. In a recent phase 1/2 clinical trial, a genetically engineered herpes simplex virus called RP1 was injected directly into melanoma tumors—whether they were on the skin, under it, or even buried deeper in organs like the lungs or liver. The results were striking. Tumors that didn’t even get the injection began to shrink, suggesting the treatment is sparking a body-wide immune attack on cancer cells.
This breakthrough is especially exciting because about half of all advanced melanoma cases can’t be tackled effectively with existing immunotherapies. Patients in the trial first received a combination of RP1 and the immune drug nivolumab every two weeks. After eight cycles, they continued with nivolumab alone for up to two years. Around one-third of the 140 participants responded positively, with their tumors shrinking by more than 30 percent in roughly 80 to 90 percent of these cases.
Importantly, this modified herpes virus doesn’t cause herpes outbreaks in patients. Instead, it targets and bursts cancer cells, releasing immune triggers that help the body hunt down tumors elsewhere. The FDA has already granted this therapy priority review, with a decision expected by July 2025. If approved, it could become only the second virus-based cancer treatment in the U.S., and the first capable of tackling tumors beyond the skin and lymph nodes. A larger phase 3 trial is now underway, offering real hope for patients who’ve run out of options.
DOI: 10.1200/JCO.2025.43.16_suppl.9537
Trial : NCT03767348
