RP1: An Emerging Intratumoral Therapy

The conversation highlights RP1, an oncolytic virus therapy showing promising systemic responses in melanoma, particularly in both injected and noninjected tumors—a notable improvement over earlier oncolytic viruses like T-VEC. The ability to inject visceral tumors under ultrasound guidance expands patient eligibility beyond superficial or in-transit lesions, potentially increasing the therapy’s role in second-line and beyond treatments. Although early data are encouraging, clinicians are awaiting longer-term follow-up to confirm durability of responses compared with other modalities such as T-cell therapies.

There are practical clinical questions around RP1 administration, such as whether to inject the full dose into 1 dominant tumor or spread it across multiple lesions to enhance bystander effects, and how critical strict 2-week dosing intervals are given logistical challenges in many clinical settings. These real-world considerations are especially relevant as many institutions share interventional radiology resources, which can complicate scheduling. Ongoing trials such as IGNITE3 are expected to shed light on these dosing and administration questions.

Overall, the enthusiasm for RP1 stems from its potential to elicit systemic immune responses even from localized injections, addressing past limitations of oncolytic viruses. However, further mature data and practical experience will be important to optimize its use and understand its place alongside other emerging melanoma therapies.