Innovative Modified Herpes Virus Shows Promise in Melanoma Treatment

In a groundbreaking development in cancer therapy, researchers have engineered a modified version of the herpes simplex virus, known as RP1, which has demonstrated the ability to shrink advanced melanoma tumors during recent clinical trials. The findings were presented at the 2025 American Society of Clinical Oncology (ASCO) meeting, highlighting a potential new avenue for treating one of the most aggressive skin cancers.

The phase 1/2 clinical trial involved 140 participants suffering from advanced melanoma, a cancer that ranks as the fifth most common among adults in the United States. This study, which included patients with tumors located both on the skin and deeper within the body, revealed that approximately one-third of the subjects responded positively to the treatment. According to Dr. Gino Kim In, a medical oncologist at the University of Southern California and key researcher in the study, the therapy’s efficacy suggests that RP1 may effectively target cancer cells throughout the body, not just those directly injected with the treatment.

Dr. In stated, "This result suggests that RP1 is effective in targeting cancer throughout the entire body and not just the injected tumor, which expands the potential effectiveness of the drug because some tumors may be more difficult or impossible to reach."

The RP1 therapy, which received priority review from the U.S. Food and Drug Administration (FDA) earlier this year, is designed to be used in combination with nivolumab (brand name Opdivo), a well-known immune checkpoint inhibitor. This dual approach aims to enhance the immune response against melanoma cells. Initial results indicate that among patients who responded positively, 80 to 90 percent experienced a tumor reduction of over 30 percent after receiving injections of both RP1 and nivolumab, administered biweekly for eight cycles before continuing with nivolumab alone for up to two years.

Despite the promising results, the findings have yet to undergo peer review. Nonetheless, they offer hope for patients with treatment-resistant advanced melanoma. Dr. In emphasized the significance of these results, stating, "The survival rate of untreatable advanced melanoma is only a few years, so this new therapy offers hope to patients who may have run out of options to fight the cancer."

The RP1 therapy is being developed by Replimune Group, Inc., a biotechnology firm specializing in oncolytic virus therapy, which utilizes modified viruses to selectively infect and destroy cancer cells while sparing healthy tissue. Previous studies suggest that oncolytic viruses can stimulate a robust immune response by causing infected cancer cells to burst, thereby releasing antigens that activate the immune system against the tumor.

As of now, the FDA has only approved one other virus-based cancer treatment, Imlygic, which is limited to tumors located on the skin or in lymph nodes. If RP1 gains approval, it could represent a significant advance in the treatment options available for patients battling advanced melanoma, particularly those who have not responded to existing immunotherapy treatments.

Looking ahead, a phase 3 trial involving over 400 participants is currently in progress to further evaluate the safety and efficacy of this innovative therapy. The FDA has set a target action date for its review of RP1 and nivolumab for July 22, 2025, which will determine whether this promising treatment becomes available to patients in the near future. Dr. In concluded, "I believe that oncolytic viruses will open up an important new approach to fighting cancer in some patients in the near future."