Avacta Group (AIM: AVCT) delivers preCISION payload data that challenges Enhertu and Datroway tumor selectivity at Science Day 2026

Avacta Therapeutics (AIM: AVCT) on May 6, 2026 unveiled comparative pharmacology data positioning its preCISION tumor-activated delivery platform against two of the most commercially significant antibody-drug conjugates on the market, Daiichi Sankyo and AstraZeneca’s Enhertu and Datroway, alongside fresh in vivo evidence that its dual-payload program AVA6207 produces durable complete responses where deruxtecan-based ADCs allow tumor regrowth. The disclosures, made at the Company’s Science Day 2026 event at the Royal Society of Chemistry in London, reframe Avacta’s preclinical narrative from a standalone platform story into a direct mechanism comparison against the deruxtecan ADC franchise that Daiichi expects will reach 700,000 eligible patients by fiscal 2030. Avacta Group shares are trading at 77.14p on the London Stock Exchange, near the upper band of a wide 26.00p to 84.00p 52-week range that reflects a sharp 2026 recovery for the AIM-listed biotech. The data release lands at a moment when the global ADC payload-delivery debate has shifted from antibody specificity to tumor selectivity, the precise terrain Avacta is now claiming with quantitative pharmacology benchmarks. For a clinical-stage developer with a market capitalisation around £349 million, anchoring its mechanism to two blockbuster comparators is a deliberate signal to investors and licensing partners.

Why is Avacta benchmarking AVA6103 against Enhertu and Datroway in the tumor-targeted topoisomerase I inhibitor category?

The AVA6103 program now sits at the centre of Avacta’s scientific positioning because it shares a payload class with the most clinically validated ADC franchise in oncology. Enhertu and Datroway both deliver deruxtecan, a topoisomerase I inhibitor, and AVA6103 delivers exatecan, a closely related topoisomerase I inhibitor. By restricting the comparison to the same payload class, Avacta is isolating the variable that matters commercially, which is the delivery mechanism rather than the cytotoxic chemistry. The Company reported that exatecan released from AVA6103 reaches peak tumor concentration in minutes, while deruxtecan released from Enhertu or Datroway reaches peak concentration after more than 24 hours, a kinetic difference that translates into more than a one-log higher maximal tumor concentration of free payload from AVA6103.

The tumor selectivity index, defined as the area-under-the-curve ratio between tumor and plasma exposure, was reported as at least three times higher for released exatecan from AVA6103 than for released deruxtecan from either Enhertu or Datroway. This is the analytical heart of the announcement. Tumor selectivity is the parameter that governs the therapeutic window in cytotoxic oncology, and a three-fold improvement on the reference standard, if reproduced in clinical settings, would be a structurally meaningful advantage. Avacta has indicated it intends to publish these comparisons at an upcoming academic meeting and in a peer-reviewed journal, which is the appropriate validation pathway for claims of this magnitude. Until peer review lands, the data should be read as preclinical signal rather than clinical proof, but the framing is unambiguous.

What does the AVA6207 dual-payload data signal about Avacta’s competitive position against deruxtecan-based ADCs?

The AVA6207 update is, in some ways, the more strategically important of the two disclosures because it tackles a known limitation of single-payload ADCs, which is tumor heterogeneity and the regrowth of resistant clones. Avacta reported that in a HEK-FAP model with high fibroblast activation protein expression, AVA6207 produced deep and durable complete responses in settings where conventional cytotoxic therapy allowed tumors to regrow. More notably, in a fibroblast activation protein-low and HER2-positive patient-derived xenograft model of gastric cancer, AVA6207 generated durable responses while Enhertu allowed tumor regrowth in the same model. The implication is that combining preCISION-delivered payloads can address mixed-biology tumors that single-target ADCs cannot fully clear.

This is the first time Avacta has reported a head-to-head efficacy advantage over a single-payload ADC in a HER2-positive patient-derived model, and the choice of comparator matters. Enhertu is the current standard-bearer in HER2-positive disease and Daiichi Sankyo and AstraZeneca have been steadily moving the franchise into earlier lines of therapy across breast, gastric, and non-small cell lung cancer. A preclinical signal that a dual-payload preCISION construct can generate durable responses where Enhertu does not, even if confined to a specific tumor model, gives Avacta a credible scientific hook for partnership conversations with the very companies competing in the deruxtecan ecosystem. Whether the gastric cancer model translates to human disease is a separate and considerably harder question, but the directional claim is now on the record.

How does the preCISION mechanism differentiate from antibody-drug conjugate payload release in solid tumors?

The technical distinction Avacta is pressing is the substrate of activation. Antibody-drug conjugates rely on antibody binding to a tumor antigen, internalisation, and intracellular cleavage to release the payload, and the kinetics of that process are governed by antigen density, internalisation rate, and lysosomal processing. The preCISION platform instead uses fibroblast activation protein, an extracellular protease upregulated in the stroma of most solid tumors but largely absent in healthy tissue, as the activation trigger. This shifts payload release from inside the cancer cell to the tumor microenvironment, which Avacta argues produces faster local concentration and reduces systemic exposure independent of the antibody target.

The strategic advantage of decoupling delivery from a specific antigen is breadth of applicability. Enhertu requires HER2 expression, Datroway requires TROP2 expression, and each ADC programme is essentially captive to its target biomarker. A preCISION construct can in principle be developed against any solid tumor with sufficient fibroblast activation protein expression in the stroma, which Avacta cites as the majority of solid tumors. This is the basis for the Company’s claim that preCISION offers tumor-selective delivery regardless of antigen target. The flip side of that breadth is that the preCISION mechanism must demonstrate consistent fibroblast activation protein-driven activation across heterogeneous tumor types in human patients, which is precisely the evidence that clinical translation will need to produce.

What execution and capital risks remain for Avacta as it pushes preCISION toward clinical validation?

The principal execution risk is the gap between preclinical pharmacology and clinical efficacy in human patients. Tumor selectivity indices generated in mouse models do not always survive translation into the heterogeneous biology of human cancers, and AVA6103 and AVA6207 will need to demonstrate that the kinetic and selectivity advantages observed preclinically produce meaningful clinical benefit relative to comparators that already have real-world efficacy data and approved labels. The bar to displace Enhertu in HER2-positive breast cancer is exceptionally high, given Daiichi Sankyo’s projected fiscal 2026 Enhertu sales of approximately $4.6 billion and the franchise’s expanding label across breast, gastric, and lung indications.

Capital is the second consideration. Avacta has raised funds multiple times in recent years, including a £16 million oversubscribed placing referenced in earlier disclosures, and clinical-stage biotechs developing platform technologies typically require sustained financing through to either a pivotal partnership or a clinical readout that can support licensing. The Company’s negative price-to-earnings ratio reflects its pre-revenue clinical-stage status, and the investment case rests on the optionality embedded in the preCISION platform rather than near-term cash generation. Investors should weigh the strength of the preclinical signal against the capital cycle that will be required to convert it into clinical proof, and against the competitive intensity of an ADC market where Daiichi Sankyo, AstraZeneca, Pfizer through its Seagen acquisition, and a growing field of next-generation conjugate developers are all advancing programmes simultaneously.

How might the Science Day disclosures reshape Avacta’s partnership and licensing optionality?

Avacta has been positioning itself for a partnership conversation rather than a go-it-alone clinical strategy, and the Science Day disclosures are tailored for that audience. Comparative pharmacology against Enhertu and Datroway is the kind of data that licensing-minded acquirers and large pharma business development teams use to triangulate platform value. Daiichi Sankyo’s stated ambition to expand its ADC reach from 120,000 patients in fiscal 2025 to 700,000 by fiscal 2030 implies a sustained appetite across the industry for delivery technologies that can extend or differentiate ADC franchises, and Avacta is presenting preCISION as a mechanism that complements rather than directly substitutes for antibody-driven delivery.

The intellectual property cadence Christina Coughlin referenced in the announcement is also relevant. A pre-clinical biotech building a defensible patent estate around a tumor-activated delivery substrate creates leverage in licensing discussions because the platform can be applied across multiple payloads and indications without renegotiating the foundational chemistry. Whether that translates into a near-term deal depends on factors outside the scientific data, including the pace of Avacta’s own clinical programmes, the bidding dynamics among potential partners, and the broader ADC dealmaking environment. The Science Day data does not by itself trigger a transaction, but it sharpens the case that preCISION is a platform worth diligencing.

Key takeaways on what this development means for Avacta, its competitors, and the antibody-drug conjugate industry

• Avacta has shifted preCISION from a standalone platform pitch to a direct mechanism comparison against the most commercially validated ADC franchise in oncology, which is a deliberate move to anchor partnership and licensing conversations.
• The reported three-fold tumor selectivity advantage and one-log higher peak tumor concentration of exatecan from AVA6103 versus deruxtecan from Enhertu and Datroway, if validated in peer review and clinical translation, would be a structurally significant pharmacology signal.
• The AVA6207 dual-payload data showing durable responses in a HER2-positive gastric cancer model where Enhertu allows regrowth gives Avacta its first head-to-head efficacy claim against a deruxtecan-based ADC, even though it remains a preclinical model result.
• Daiichi Sankyo and AstraZeneca’s deruxtecan franchise faces no immediate threat from preclinical Avacta data, but the disclosures introduce a competitive narrative that will require monitoring as preCISION constructs progress through clinical development.
• The preCISION mechanism’s reliance on fibroblast activation protein in the tumor stroma rather than a specific tumor antigen is the basis for Avacta’s claim that the platform is target-agnostic, which is the strategic basis for breadth across solid tumors.
• Tumor selectivity is the parameter that defines the therapeutic window in cytotoxic oncology, and Avacta is now claiming a quantitative advantage on this metric against the reference standard, which is the most credible pharmacology positioning the Company has presented to date.
• Avacta Group shares trading near 77p, close to the upper band of a 26.00p to 84.00p 52-week range, reflect a sharp 2026 recovery and a market capitalisation around £349 million that prices the optionality of platform validation rather than near-term clinical cash flows.
• Clinical-stage biotechs presenting comparative pharmacology against approved blockbusters carry significant translation risk, and the gap between mouse model selectivity indices and human clinical benefit remains the central execution challenge for AVA6103 and AVA6207.
• The intellectual property cadence Christina Coughlin highlighted positions Avacta for licensing leverage across multiple payloads and indications, which matters more for valuation than any single programme readout.
• The broader ADC industry, with Daiichi Sankyo targeting 700,000 eligible patients by fiscal 2030 and Pfizer integrating its Seagen acquisition, continues to demand differentiated delivery technologies, and preCISION now has a sharper claim on that conversation than it did before Science Day 2026.