HER2-targeting therapies are commonly administered in combination regimens for metastatic breast cancer. Demonstrating that ES2B-C001 is safe - and potentially adds efficacy - when combined with ESMO guideline recommended treatment regimens for advanced-stage breast cancer such as Enhertu® (trastuzumab deruxtecan) could significantly enhance the commercial and licensing potential of ExpreS2ion's breast cancer program. This update to the phase I study protocol also supports broader patient eligibility and aligns with current treatment standards.

While the combination trial was initially intended for the vaccine's later-phase clinical development, the recent approval of reimbursement of Enhertu® by Austrian health authorities as a treatment for HER2-positive metastatic breast cancer creates an opportunity to accelerate the generation of these important data.

This amendment also requests to increase the number of clinical trial sites in Austria. To further support patient enrolment, referral pathways have been expanded through agreements with five clinics in Vienna to directly refer eligible patients to the active study site.

Upon approval, which is anticipated by mid-Q3 2025, ExpreS2ion anticipates that these protocol modifications will substantially accelerate recruitment for the ongoing Phase I trial. Importantly, the trial will recruit patients under the current protocol, and these amendments are not expected to change existing timelines. The Company remains on track to report interim safety and tolerability data from the first patient cohort in the ES2B-C001 Phase I study and will provide an update on timelines when the first patient has been dosed.

About ES2B-C001 (HER2-VLP)
ES2B-C001 is an innovative therapeutic vaccine developed specifically for HER2-expressing cancers. This novel approach combines ExpreS2ion's ExpreS2 production platform with AdaptVac's VLP technology, both of which have been proven in clinical Phase III. The HER2-VLP vaccine's design aims to stimulate a robust and durable polyclonal immune response against HER2-expressing tumours, offering a complementary strategy to current treatments. Preclinical studies, as highlighted by Ruzzi et al. (2022), have demonstrated the vaccine's safety and efficacy across multiple animal models, significantly inhibiting tumour growth and improving survival rates. By leveraging the patient's immune system, ES2B-C001 addresses the complexities of HER2-expressing breast cancers, potentially offering enhanced therapeutic options and filling critical gaps in the current treatment landscape.

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