Cancer Therapy OST-HER2 Faces 2026 EMA Call After Survival Data

Key Takeaways

• EMA CAT/CHMP/PRAC initiated Continuous Evaluation (rolling review) of the OST-HER2 CMA dossier, disclosed April 30, 2026.
• Phase 2b final 2-year OS: 75% (27/36) vs 40% published historical control (p < 0.0001), per company SEC 10-K narrative.
• EMA aligned that 3-year OS data (early Q4 2026) complete CMA evaluation; company targets a potential Q4 2026 decision.
• Comparisons use historical controls, not a randomized contemporaneous arm—an important evidence caveat for HTA and investors.

What triggered the 2026 EMA call for OST-HER2?

OS Therapies announced that EMA’s Committee for Advanced Therapies, working with CHMP and PRAC, started Continuous Evaluation of a Conditional Marketing Authorisation request for OST-HER2 to prevent or delay recurrence after complete resection of pulmonary metastatic osteosarcoma.

The primary disclosure is the company’s SEC exhibit (April 30, 2026). The same filing notes selection into EMA’s Raw Data Pilot with the Scientific Advice Working Party.

Which survival numbers underpin the osteosarcoma package?

In its Form 10-K discussion of the Phase 2b program, OS Therapies reported final two-year overall survival among 36 evaluable patients: 75% (27 of 36) alive two years after the most recent pulmonary resection, versus 40% in a published control population (p < 0.0001).

That narrative is in the company’s SEC Form 10-K. The study was not powered as a randomized controlled trial; survival comparisons rely on published historical data rather than a matched contemporary control arm.

How will EMA sequence 2.5-year and 3-year overall survival?

Per the April 30 rolling-review announcement, EMA and the company agreed that 3-year overall survival will complete CMA evaluation. EMA also requested updated 2.5-year OS data expected by mid–second quarter 2026, with 3-year OS due early in the fourth quarter of 2026.

• Already submitted: 2-year OS package.
• Mid-Q2 2026: updated 2.5-year OS.
• Early Q4 2026: 3-year OS to finish the CMA dossier.
• Company outlook: potential CMA decision in Q4 2026.

What else is moving in parallel for European access?

OS Therapies said UK NICE and EMA Health Technology Assessment interactions have started alongside the regulatory clock, aiming to shorten the gap between any authorization and reimbursement. International coordination under an EMA–FDA information-sharing programme was also flagged.

For context on EU advanced-therapy review pathways, see EMA’s public materials on advanced therapy medicinal products.

Why OST-HER2 matters for rare sarcoma pipelines

Metastatic osteosarcoma after lung metastasectomy still lacks modern immunotherapy standards in many markets. OST-HER2 is positioned as a gene-edited Listeria vector designed to stimulate anti-HER2 immunity after surgical clearance of pulmonary disease.

Company filings also note EMA orphan, Fast Track, and ATMP designations historically attached to the program, reinforcing rarity and regulatory novelty—not approval.

What remains unproven before a 2026 CMA decision?

Historical-control OS gains can look strong and still fail confirmatory standards. EMA may still raise manufacturing, potency, immunogenicity, or external-control bias questions during rolling review. A Q4 2026 decision is the company’s target, not an agency commitment.

Until CHMP issues a positive opinion and the European Commission grants conditional authorization, OST-HER2 remains investigational in the EU.

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Frequently Asked Questions

Primary Sources

1. SEC — OS Therapies EMA rolling review exhibit (April 30, 2026)
2. SEC — OS Therapies Form 10-K (2-year OS 75% vs 40%)
3. EMA — Advanced therapies regulatory overview