Intratumoral cancer therapies market has a peculiar problem that has nothing to do with whether the drugs work. It has to do with whether anyone can prove they work using the tools oncology already trusts. In August 2026, the FDA granted accelerated approval to vusolimogene oderparepvec, an engineered herpes simplex virus injected directly into melanoma lesions, in combination with nivolumab.
The approval was a milestone. It was also accompanied by an unusually candid regulatory record: FDA reviewers stated plainly that the single-arm IGNYTE trial’s response assessment methodology “artificially increased” the reported objective response rate and duration of response, and that RECIST was never designed for intratumoral therapy in the first place. The drug is approved. The measurement problem is not solved.
The Injection Site Is Not the Story
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What makes intratumoral therapy intellectually compelling is also what makes it regulatorily awkward.
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A clinician injects a lesion. The lesion shrinks. But the lesion was injected of course it shrank. The real question is whether the immune system learned something it can carry elsewhere.
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FDA’s own briefing documents acknowledge this tension explicitly: responses in injected lesions may reflect “local oncolytic activity, local immune activation, or injection-related volume changes,” and distinguishing local from systemic effect is not straightforward.
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In the IGNYTE trial supporting the approval, 57.7% of injected lesions and 41.3% of noninjected lesions resolved completely, a pattern the sponsor argued demonstrated systemic activity.
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FDA remained unconvinced that the contribution of the virus could be isolated from nivolumab in a single-arm design. The approval moved forward on unmet need, but the evidentiary foundation is thinner than the enthusiasm surrounding it.
Melanoma Is the Proving Ground, Not the Destination
Nearly every serious conversation about intratumoral therapy begins and ends with melanoma, and for understandable reasons. The lesions are accessible. The disease is immunologically visible. And the unmet need after anti-PD-1 failure is genuine. A real-world compassionate-use experience from Hospital Clinic Barcelona, presented in 2025, reported objective responses in 7 of 11 patients receiving intratumoral RP1, with four complete responses and a median progression-free survival of 6.18 months. These are not trivial numbers for a population with few options.
But liver tumors tell a different story. A 2026 review in Frontiers in Oncology concluded that intratumoral therapies for hepatocellular carcinoma and liver-dominant metastases have produced “heterogeneous outcomes,” with several large studies failing to demonstrate survival benefit, largely because the liver’s immune microenvironment is tolerogenic in ways that melanoma’s is not. The same delivery strategy, the same biological rationale, a fundamentally different organ. The field’s melanoma success has not yet traveled.
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What the Next Generation Is Actually Testing
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The mechanistic ambition has moved beyond oncolytic viruses. A phase I/II study published in Cancer Discovery in 2026 tested intratumoral sotigalimab, an anti-CD40 agonist, combined with pembrolizumab in 32 checkpoint-naïve melanoma patients. The objective response rate was 50%, with a disease control rate of 92%, and responses were observed in both injected and noninjected tumors.
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Multiomic analysis showed activation of antigen-presenting cells and expanded T-cell clones shared across lesions. This is the abscopal effect with a molecular paper trail the kind of evidence that might eventually persuade regulators that something systemic is happening.
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Separately, ultrasound-responsive micro/nanobubble cavitation is being explored as a physical rather than biological means of enhancing intratumoral drug penetration, using mechanical forces to transiently permeabilize tumor vasculature and improve distribution.
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These are not incremental tweaks. They represent different theories of what intratumoral therapy is for: immune priming in one case, delivery optimization in the other.
The Biopsy Is the Real Product
Perhaps the most underdiscussed shift in this space is epistemological rather than therapeutic. Intratumoral trials increasingly mandate baseline and on-treatment biopsies not as optional correlates but as essential components of the evidence package. The IGNYTE review noted that biopsies were required at baseline and at Study Day 43, and that in no instance did a biopsy or excision of a lesion remnant improve the best overall response.
The biopsy did not change the outcome. It changed the interpretation. As intratumoral therapies proliferate dendritic cell vaccines like ilixadencel, nanoparticle cisplatin formulations, STING agonists the field is quietly building a repository of tissue-based evidence that may ultimately matter more than any single response rate. The injection is the intervention. The biopsy is the argument.
A Field That Must Learn to Lose Well
Intratumoral cancer therapies market will not be built on unqualified wins. It will be built on the discipline to distinguish necrosis from response, local control from systemic immunity, and approval from proof. The RP1 episode is instructive precisely because it refused to resolve cleanly.
A therapy can reach patients while its evidence base remains contested. The question is whether the next generation of trials randomized, biopsy-anchored, and honest about what RECIST cannot measure will do the harder work of showing not just that a tumor shrank, but that the immune system remembers why.