Surrogate Endpoints in Tigilanol Tiglate Clinical Trials: Beyond Tumour Response Rate
Why oncology trials of intralesional tigilanol tiglate may benefit from surrogate endpoints — and which biomarkers are plausible candidates for future studies.
Phase II and III oncology trials traditionally rely on response-based endpoints (objective response rate, progression-free survival) or survival itself. For an intralesional therapy like tigilanol tiglate (EBC-46), where the local pharmacological effect is rapid and visible, the choice of endpoint matters more than usual: investigators must decide whether they are measuring a local-control signal, a systemic-control signal, or both. Surrogate endpoints — markers that stand in for the clinical outcome of interest — may help bridge those questions.
What counts as a surrogate
A surrogate endpoint is a biomarker that can substitute for a clinically meaningful outcome when there is sufficient evidence that changes in the surrogate predict changes in the outcome. The FDA’s table of surrogate endpoints is the canonical published reference for what regulators have accepted in oncology and other fields. In oncology, accepted surrogates include progression-free survival (PFS) for some tumour types, pathological complete response in neoadjuvant trials, and minimal residual disease in haematological cancers.
Surrogates are particularly attractive when overall survival follow-up is long (because new lines of therapy after progression confound the survival signal) or when the investigational therapy operates locally and a tissue-level readout is more biologically informative than a downstream survival reading.
Plausible candidates for tigilanol tiglate trials
Given the local mechanism of intralesional tigilanol tiglate, several surrogate categories deserve consideration:
1. Lesion-level response by imaging (RECIST-based or volumetric MRI) for the injected target lesion. This is straightforward but only reflects local activity at the treated site.
2. Time to local recurrence at the injected site. For a local therapy, this is a clinically meaningful intermediate endpoint that captures durability of response.
3. Pathological response rate when the lesion is excised after treatment, which can quantify residual viable tumour cells under the microscope.
4. Pharmacodynamic biomarkers in serum. PKC activation in tumour-associated immune cells, transient cytokine spikes (TNFα, IL-6, IL-8), and circulating tumour DNA (ctDNA) clearance are potentially useful. Background on intralesional tigilanol tiglate biology is summarised by QBiotics Group.
5. Patient-reported outcomes (PROs) measuring symptom burden at the injected lesion. While not strictly a surrogate for survival, validated PROs can support a regulatory case in supportive-care indications and palliative settings.
Pitfalls of surrogates in this setting
A surrogate is only useful if its relationship to the clinical outcome of interest has been validated. In small, single-arm, or early-phase studies, that validation step is often missing. The European Medicines Agency guideline on the evaluation of anticancer medicinal products in man is explicit about this risk: a surrogate that correlates with outcome in observational data may still fail to predict treatment effect in randomised trials. Tigilanol tiglate trials should therefore pre-specify which endpoints are regulatory-grade and which are supportive.
Local-control surrogates also do not capture the question of whether bystander immune effects translate into systemic disease control. If the immunological hypothesis is being tested, biomarkers of T-cell activation, tumour-associated antigen-specific responses, and abscopal lesion shrinkage in non-injected sites need to be pre-specified rather than reported as exploratory afterthoughts.
Distinction from oral supplement formats
All of the above is specific to intralesional pharmaceutical-grade tigilanol tiglate in clinical trials. Whole-seed blushwood berry extract sold as a dietary supplement (for example, the products at Blushwood Health) is not an investigational pharmaceutical. The supplement category is governed by DSHEA in the United States and equivalent food-supplement frameworks elsewhere, with no approved therapeutic indications and no requirement for clinical efficacy trials. Surrogate endpoints have no application to supplement marketing.
Related Articles
Related coverage: progression-free survival endpoints in tigilanol tiglate trials and quality-of-life and patient-reported outcomes.
This article is for informational purposes only and is not medical advice.
