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In a promising development in cancer therapy, scientists have genetically modified the herpes simplex virus (HSV-1) to target and shrink deadly melanoma tumors—even those deep within the body. The therapy, called RP1, was tested in combination with the immune drug nivolumab in a phase 1/2 clinical trial involving 140 patients with advanced melanoma. About a third of patients responded to the treatment, with 80–90% experiencing tumor shrinkage greater than 30%.Unlike the previously approved virus-based therapy Imlygic, which is limited to skin or lymph node tumors, RP1 shows potential to reach and treat tumors in less accessible areas like the liver or lungs. This approach, known as oncolytic virus therapy, leverages the virus's ability to selectively infect and destroy cancer cells, triggering a broader immune response without harming healthy tissue.The FDA has granted RP1 priority review, with a decision expected by July 22, 2025. If approved, it could become a powerful new option for patients with treatment-resistant melanoma, a form of cancer that currently lacks effective therapies for nearly half of advanced cases. A phase 3 trial with over 400 participants is now underway to further evaluate its potential.Follow Science Sphere for regular scientific updates.RESEARCH PAPER 📄Gino Kim In et al, "Response analysis for injected and non-injected lesions and of the safety and efficacy of superficial and deep/visceral RP1 injection in the registrational cohort of anti–PD-1–failed melanoma patients of the IGNYTE trial.", Journal of Clinical Oncology (2025)