On July 16, 2026 Greenwich LifeSciences, Inc. (Nasdaq: GLSI) (the "Company"), a clinical-stage biopharmaceutical company focused on its Phase III clinical trial, FLAMINGO-01, which is evaluating GLSI-100, an immunotherapy to prevent breast cancer recurrences, reported the following update on the combination of both HLA-A*02 and non-HLA-A*02 patients in FLAMINGO-01 in Europe.

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All European and US Sites to Combine All Patients Independent of HLA Type in the Randomized Arms of FLAMINGO-01

The Company previously announced that US clinical sites started enrolling both HLA-A*02 and non-HLA-A*02 patients in the same randomized arms in FLAMINGO-01, based on the FDA’s review of such protocol changes, effectively more than doubling the enrollment rate of the pivotal arm of the study. Non-HLA-A*02patients who represent about 55% of the population and were on waiting lists for up to a year are now eligible for enrollment.

The European Medicines Agency (EMA) has completed their review and will also allow the combination of both HLA-A*02 and non-HLA-A*02 patients in Europe. Thus, all 170-180 clinical sites in the US and Europe, are now operating under the same protocol and could continue enrolling up to the first interim analysis. Data can be analyzed by individual HLA types as well.

Additional feedback is expected from UK and Canadian regulators. The Company plans to provide updates regarding the resulting improved trial design, including a pathway for the Company to now pursue approval for both HLA-A*02 and non-HLA-A*02 patients using the increased statistical power of a combined analysis of the two patient groups together potentially doubling the market for GP2 by accelerating the clinical development of the non-HLA-A*02 population.

About FLAMINGO-01 Open Label Phase III Data

More than 1,300 patients have been screened with a current screen rate of approximately 800 patients per year. The 250 patient non-HLA-A*02 arm is now fully enrolled, where all patients received GLSI-100, which is 5 times more treated patients and recurrence rate data than the approximately 50 patients treated in the Phase IIb trial. The Primary Immunization Series (PIS), which includes the first 6 GLSI-100 injections over the first 6 months and is required to reach peak protection, is followed by 5 booster injections given every 6 months to prolong the immune response, thereby providing longer-term protection.

In the non-HLA-A*02 arm, a preliminary analysis of recurrence rates after the PIS is completed shows an approximately 70-80% reduction in recurrence rate.
This observation is trending similarly to the Phase IIb trial results and hazard ratio where HLA-A*02 patients were treated and where breast cancer recurrences were reduced up to 80% compared to a 20-50% reduction in recurrence rate by other approved products.
The immune response at baseline prior to any GLSI-100 treatment, the increasing immune response during the PIS, and the safety profile of non-HLA-A*02 patients is trending similarly to the HLA-A*02 arms of FLAMINGO-01 and to the Phase IIb study.
The AACR (Free AACR Whitepaper) Meeting 2026 delayed-type-hypersensitivity (DTH) poster and the ASCO (Free ASCO Whitepaper) Meeting 2026 injection site reaction (ISR) poster can be seen and downloaded at the bottom of the Phase III clinical trial tab on the Company’s website here.
As shown in both posters the frequency of DTH and ISR reactions increased statistically significantly over time.
As reported in Table 1 of each poster, each HLA-A type exhibited more frequent immune reactivity after treatment with GLSI-100 than at baseline.
Baseline DTH reaction prior to any treatment suggests that GP2 may be a natural antigen and that GP2 specific T cells may exist in some patients prior to any treatment with GLSI-100. Baseline immune response to GP2 prior to any vaccination with GP2 was also observed in the Phase IIb trial and is being observed in the blinded randomized arms of FLAMINGO-01, where HLA-A*02 only patients are being vaccinated.

Analysis of the open label data from FLAMINGO-01 has been conducted in a manner that maintains the study blind. The open label recurrence rate, immune response, and safety data is based on the patients enrolled to date in FLAMINGO-01 and the data provided by the clinical sites so far, which is not completed or fully reviewed, and is thus preliminary. While comparing any preliminary FLAMINGO-01 data to the Phase IIb clinical trial data may be possible, these preliminary results are not a prediction of future results, and the results at the end of the study may differ.

About GLSI-100 Phase IIb Study

In the prospective, randomized, single-blinded, placebo-controlled, multi-center (16 sites led by MD Anderson Cancer Center) Phase IIb clinical trial of HLA-A*02 breast cancer patients, 46 HER2/neu 3+ over-expressor patients were treated with GLSI-100, and 50 placebo patients were treated with GM-CSF alone. After 5 years of follow-up, there was an 80% or greater reduction in cancer recurrences in the HER2/neu 3+ patients who were treated with GLSI-100, followed, and remained disease free over the first 6 months, which we believe is the time required to reach peak immunity and thus maximum efficacy and protection. The Phase IIb posters and results can be summarized as follows and can be seen here:

80% or greater reduction in metastatic breast cancer recurrence rate over 5 years of follow-up with a peak immune response at 6 months and well-tolerated safety profile.
The PIS elicited a potent immune response as measured by local skin tests and immunological assays.

About FLAMINGO-01 and GLSI-100

FLAMINGO-01 (NCT05232916) is a Phase III clinical trial designed to evaluate the safety and efficacy of Fast Track designated GLSI-100 (GP2 + GM-CSF) in HER2 positive breast cancer patients who had residual disease or high-risk pathologic complete response at surgery and who have completed both neoadjuvant and postoperative adjuvant trastuzumab based treatment. The trial is led by Baylor College of Medicine and currently includes US and European clinical sites from university-based hospitals and academic and cooperative networks with plans to open up to 170-180 sites globally.

About Breast Cancer and HER2/neu Positivity

One in eight U.S. women will develop invasive breast cancer over her lifetime, with approximately 300,000 new breast cancer patients and 4 million breast cancer survivors. HER2 (human epidermal growth factor receptor 2) protein is a cell surface receptor protein that is expressed in a variety of common cancers, including in 75% of breast cancers at low (1+), intermediate (2+), and high (3+ or over-expressor) levels.

(Press release, Greenwich LifeSciences, JUL 16, 2026, View Source [SID1234669271])