Greenwich LifeSciences Expands GP2 Breast Cancer Vaccine Trial FLAMINGO-01 Into the UK

Greenwich LifeSciences announced that UK regulators have formally approved the company's application to expand its Phase III FLAMINGO-01 trial into the UK, adding potentially five to ten geographically distributed UK sites to the approximately 170 to 180 sites already approved across the US and Europe.¹ The expansion is being carried out in collaboration with The Royal Marsden, a leading cancer research institute, with discussions underway across multiple academic sites in London, Cambridge, Edinburgh, Oxford, Manchester, Southampton, and Cardiff, among other cities.¹

In a company announcement, Snehal Patel, chief executive officer of Greenwich LifeSciences, said, "We are very excited to be adding these UK sites from prominent research institutions. The initial introduction was driven by patient interest in the UK."¹

FLAMINGO-01 is evaluating GLSI-100, an immunotherapy combining the peptide vaccine GP2 with granulocyte-macrophage colony-stimulating factor (GM-CSF), designed to prevent breast cancer recurrence in patients with HER2-expressing tumors following standard neoadjuvant and adjuvant trastuzumab-based therapy.¹

How does GP2 work as a cancer vaccine?

GP2 is a nine-amino-acid transmembrane peptide derived from the HER2/neu protein, a cell surface receptor expressed in a variety of common cancers, including in roughly 75% of breast cancers at low, intermediate, or high expression levels.¹ Unlike HER2-targeted monoclonal antibodies such as trastuzumab, which bind directly to the HER2 receptor, GP2 works by training the patient's own immune system to recognize and attack HER2-expressing cells, administered via intradermal injection alongside GM-CSF to stimulate that immune response.¹

That immune-training mechanism is broadly characteristic of cancer vaccines as a drug class. Martin Lachs, PhD, vice-president of project management, oncology, at ICON, described this mechanism in an interview with BioPharm International^© about mRNA-based cancer vaccines: "The mRNA contained in the vaccine encodes the instructions for healthy cells to temporarily produce cancer-specific antigens. Immune cells will recognize these antigens as foreign and become trained in targeting and destroying cells that express them. This provides the immune system with an improved capacity to recognize and fight cancer cells."² Lachs's comments were made specifically about mRNA cancer vaccines, a different vaccine platform than GP2's peptide-based approach, but the underlying immunological principle, training the immune system to recognize and target tumor-associated antigens, applies across cancer vaccine platforms generally.

What clinical data support the FLAMINGO-01 program?

FLAMINGO-01 (NCT05232916) is a randomized, double-blinded, multicenter Phase III trial in HLA-A02 patients, alongside a non-randomized arm of roughly 250 non-HLA-A02 patients now fully enrolled.¹ Immune response data presented at the 2026 AACR and ASCO meetings showed that delayed-type hypersensitivity and injection site reactions, both used as measures of in vivo immune response, increased statistically significantly over time following GLSI-100 vaccination, with each HLA-A type showing more frequent immune reactivity after treatment than at baseline.¹ The company said the safety profile and immune response trends in non-HLA-A02 patients are tracking similarly to the HLA-A02 arms of the trial and to the earlier phase IIb study.¹

Why expand into the UK specifically?

The UK expansion follows a series of recent regulatory and operational updates for FLAMINGO-01. In July, European regulators approved combining HLA-A02 and non-HLA-A02 patients into the same randomized arms, following a similar change US sites had already implemented based on FDA review, a change the company said has more than doubled the pivotal arm's enrollment rate in the US.³ Separately, the company received European approval for use of commercially manufactured GP2 in the trial.¹ Greenwich's Data Safety Monitoring Board met in May 2026 and recommended the study continue without modification, and the trial's Steering Committee endorsed planned protocol modifications discussed at the San Antonio Breast Cancer Symposium in December 2025.⁴

What happens next?

With UK site approval now secured, Greenwich LifeSciences' next step is finalizing site activation across the identified UK cities and continuing enrollment across its now-expanded global site network.

References

1. Greenwich LifeSciences Announces Approval to Expand FLAMINGO-01 into the United Kingdom. (2026 Jul 22). GlobeNewswire. https://www.globenewswire.com/news-release/2026/07/22/3331163/0/en/greenwich-lifesciences-announces-approval-to-expand-flamingo-01-into-the-united-kingdom.html
2. Mirasol, F. (2024 Jan 1). From Vaccines to Oncology and Beyond: Tracking mRNA's Progress. BioPharm International. https://www.biopharminternational.com/view/from-vaccines-to-oncology-and-beyond-tracking-mrna-s-progress
3. Greenwich LifeSciences Announces European Approval for Combining Both HLA Populations in FLAMINGO-01. (2026 Jul 16). GlobeNewswire. https://www.globenewswire.com/news-release/2026/07/16/3328362/0/en/Greenwich-LifeSciences-Announces-European-Approval-for-Combining-Both-HLA-Populations-in-FLAMINGO-01.html
4. Greenwich LifeSciences Provides Clinical Updates on FLAMINGO-01. (2026 Jul 20). GlobeNewswire. https://www.globenewswire.com/news-release/2026/07/20/3329545/0/en/Greenwich-LifeSciences-Provides-Clinical-Updates-on-FLAMINGO-01.html