Greenwich LifeSciences Announces Preliminary Analysis Showing 80% Recurrence Rate Reduction in the Open Label Arm of FLAMINGO-01

Rhea-AI Summary

Greenwich LifeSciences (Nasdaq: GLSI) reported a preliminary analysis from the open-label non-HLA-A*02 arm of FLAMINGO-01 showing an approximately 80% reduction in recurrence rate in the fully enrolled 250-patient arm by two analytic methods. Method 1 compared treated patients after the Primary Immunization Series to historical T-DM1 (KATHERINE) recurrence rates; Method 2 compared recurrence during the 6-month PIS (100 patient-years) to post-PIS follow-up (132 patient-years). The first patient completed all primary and booster vaccinations. Results are preliminary, the arm has no direct placebo comparator, and data are not completed or fully reviewed.

Positive

• ~80% observed recurrence-rate reduction in 250 patients
• Cohort size 250 (≈5× Phase IIb treated patients)
• First patient completed full PIS plus booster series
• Immune response and safety trending similarly to Phase IIb

Negative

• Open-label non-HLA-A*02 arm has no placebo comparator
• Post-PIS follow-up equals 132 patient-years (≈15% of max)
• Preliminary data not completed or fully reviewed

Key Figures

Recurrence reduction approximately 80% Preliminary analysis in 250-patient non-HLA-A*02 arm of FLAMINGO-01

Non-HLA-A*02 arm size 250 patients Fully enrolled open-label arm in FLAMINGO-01

TDM1 recurrence rate 3.5–4% per year or higher Historical recurrence rate in Katherine study TDM1 arm

Exposure during PIS 100 patient years First 6 months vaccination period in non-HLA-A*02 arm

Exposure after PIS 132 patient years Follow-up after completion of PIS in non-HLA-A*02 arm

Vaccination series length 11 vaccinations over 3 years Primary and booster GLSI-100 series for first non-HLA-A*02 patient

Primary Immunization Series 6 injections over 6 months Initial GLSI-100 dosing to reach peak protection

Booster injections 5 boosters every 6 months Injections after PIS to prolong immune response

Market Reality Check

$10.73 Last Close

Volume Volume 154,664 is about 2.0x the 20-day average of 80,375, indicating elevated interest ahead of this update. high

Technical Trading at $10.73, modestly above the 200-day MA of $10.23 and 25.85% below the 52-week high of $14.47.

Peers on Argus 1 Up

Peers in Biotechnology showed mixed moves, with names like CLYM up 29.87% and ACOG down 10%, while GLSI was down 4.79% pre-news, pointing to stock-specific dynamics rather than a broad sector trend.

Historical Context

Date	Event	Sentiment	Move	Catalyst
Dec 08	Enrollment milestone	Positive	+7.5%	Completed enrollment in 250-patient open-label non-HLA-A*02 arm.
Dec 03	Trial operations update	Positive	+5.1%	Provided global screening update with 1,000+ patients and 140 sites.
Oct 09	Geographic expansion	Positive	-2.3%	Added Austria to FLAMINGO-01 following European regulator approval.
Oct 02	Geographic expansion	Positive	+5.3%	Expanded FLAMINGO-01 to Belgium, the tenth approved country.
Sep 30	Geographic expansion	Positive	-2.1%	Received approval to expand FLAMINGO-01 to Portugal.

Pattern Detected

Recent FLAMINGO-01 updates have often seen positive price reactions, but trial expansion headlines have occasionally been followed by modest pullbacks.

Recent Company History

Over the last six months, Greenwich LifeSciences has focused updates on its Phase III FLAMINGO-01 trial. Key milestones include expanding into new EU countries (Portugal, Belgium, Austria) and screening over 1,000 patients across 140 sites. Most news carried constructive trial or enrollment progress and often aligned with positive share moves, especially the Dec 3 and Dec 8 updates tied to global screening and completion of the 250-patient non-HLA-A*02 open-label arm. Today’s preliminary efficacy signal follows directly on that enrollment milestone.

Market Pulse Summary

The stock is surging +15.1% following this news. A strong positive reaction aligns with the clearly favorable preliminary efficacy signal, where an approximately 80% reduction in recurrence is observed in the 250-patient non-HLA-A*02 arm. Historically, GLSI has often moved higher on constructive FLAMINGO-01 updates, though not uniformly. Investors would need to balance enthusiasm over these early data against the preliminary nature of the analysis and the limited 132 patient years of post-PIS follow-up.

Key Terms

immunotherapy medical

"GLSI-100, an immunotherapy to prevent breast cancer recurrences, today announced..."

Treatment that uses or enhances the body’s immune system to detect and fight disease, most often cancers or chronic infections; think of it as training or arming the body’s own soldiers to find and destroy targets. It matters to investors because successful immunotherapies can lead to high-value drug approvals, recurring revenue from long-term treatments, and changes in competitive dynamics, while failures or safety issues in clinical trials can materially affect company valuations.

HLA-A*02 medical

"open label non-HLA-A*02 arm of FLAMINGO-01."

HLA-A*02 is a common genetic variant of the HLA-A gene, which helps the immune system recognize infected or abnormal cells. Think of it as a particular model of a lock on cells that determines which immune system “keys” can fit; this matters to investors because many immunotherapies, vaccines and diagnostic tests are designed for or tested in people with this variant, affecting who is eligible for a treatment and the potential market size.

hazard ratio medical

"trending similarly to the Phase IIb trial results and hazard ratio where HLA-A*02 patients..."

A hazard ratio is a way scientists compare the chance of something happening over time between two groups, like patients taking different medicines. If the ratio is high, it means one group is more likely to experience the event sooner or more often, which helps determine how effective a treatment is or how risky a situation might be.

placebo-controlled clinical

"we will seek to continue to treat non-HLA-A*02 patients in a placebo controlled manner..."

"Placebo-controlled" describes a testing method where one group receives the actual treatment or intervention, while another group receives a harmless, inactive version called a placebo. This approach helps determine whether the real treatment has genuine effects beyond psychological expectations. For investors, understanding this ensures confidence that reported benefits are real and not influenced by bias or false perceptions.

AI-generated analysis. Not financial advice.

STAFFORD, Texas, Dec. 15, 2025 (GLOBE NEWSWIRE) -- 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, today announced an approximately 80% recurrence rate reduction in the open label non-HLA-A*02 arm of FLAMINGO-01.

• A preliminary analysis of recurrence rates by two methods to estimate the reduction in recurrence rate shows an approximately 80% reduction in recurrence rate in the fully enrolled, 250 patient non-HLA-A*02 arm of FLAMINGO-01. This arm does not have a direct placebo comparator arm, thus these two methods were used.
• 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. See the summary of the Phase IIb results below.
• The first non-HLA-A*02 patient has completed the 11 primary and booster vaccinations over the first 3 years.
  
  

In addition to announcing this first analysis of the recurrence rate data in the open label non-HLA-A*02 arm of FLAMINGO-01, the Company previously reported promising observations showing that the immune response at baseline prior to any GLSI-100 treatment, the increasing immune response during the primary immunization series, 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 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 250 patient non-HLA-A*02 data set, 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. Since the 250 non-HLA-A*02 patients do not have a placebo arm for a direct comparison, the following two methods were used, yielding the 80% reduction in recurrence rate observation:

• Method 1: The recurrence rate of these 250 treated patients after completing the PIS was compared to the expected historical recurrence rate per year reported for this population in the Katherine study who received TDM1 (Kadcyla), which is about 3.5-4% recurrences per year or higher in the initial years of the Katherine study. The majority of the treated patients in FLAMINGO-01 also received TDM1 followed by GLSI-100. The data suggests an approximately 80% reduction in recurrence rate after the GLSI-100 PIS is completed as compared to the TDM1 arm of the Katherine study at a similar timepoint.
• Method 2: The recurrence rate during the first 6 months of vaccination or PIS period when the patient may not be fully protected or protected at all, which covered an exposure period of 100 patient years, was compared to the recurrence rate after the PIS is completed and after peak immunity is believed to be achieved, which covered an exposure period of 132 patient years. The exposure period (patient years) is defined as the cumulative number of years all patients are followed in a period. The data suggests that the peak immunity is lowering the recurrence rate by approximately 80% after the PIS is completed as compared to the recurrence rate during the PIS period.
  • For the first 6 months of vaccination or PIS, the theoretical maximum patient years would be 250 patients at 0.5 years each or 125 patient years. Thus 100 completed patient years represents 80% of the maximum potential patient years and within 3 to 6 months all vaccinations during this period may be completed.
  • For the period after the PIS is completed, the theoretical maximum patient years would be 250 patients at 3.5 years of follow-up each or 875 patient years. Thus 132 completed patient years represents 15% of the maximum potential patient years and represents an average of 9 months of follow-up time after the PIS for patients who have completed the PIS.

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.

CEO Snehal Patel commented, "We are very excited to announce in our 100^th press release since going public that the first patient has completed the full primary and booster vaccination series in FLAMINGO-01. We are equally excited to see a positive trend in the recurrence rate in the non-HLA-A*02 arm of FLAMINGO-01, as assessed multiple ways, that is trending similarly to the Phase IIb trial results where HLA-A*02 patients were treated. Despite these being preliminary results that will mature and can change with time, seeing a reduction in expected recurrence rates that is trending towards a low HR of 0.2, which represents an 80% reduction in recurrence rate, is very encouraging and which is why along with the similarly promising safety and immune response data to date, we will seek to continue to treat non-HLA-A*02 patients in a placebo controlled manner in the study. We will continue to analyze the data and may provide updates at any time."

Previously Published Phase IIb Data

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 results can be summarized as follows:

• 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 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 150 sites globally. In the double-blinded arms of the Phase III trial, approximately 500 HLA-A*02 patients are planned to be randomized to GLSI-100 or placebo, and up to 250 patients of other HLA types are planned to be treated with GLSI-100 in a third arm. The trial has been designed to detect a hazard ratio of 0.3 in invasive breast cancer-free survival, where 28 events will be required. An interim analysis for superiority and futility will be conducted when at least half of those events, 14, have occurred. This sample size provides 80% power if the annual rate of events in placebo-treated subjects is 2.4% or greater.

For more information on FLAMINGO-01, please visit the Company's website here and clinicaltrials.gov here. Contact information and an interactive map of the majority of participating clinical sites can be viewed under the "Contacts and Locations" section. Please note that the interactive map is not viewable on mobile screens. Related questions and participation interest can be emailed to: flamingo-01@greenwichlifesciences.com

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.

About Greenwich LifeSciences, Inc.

Greenwich LifeSciences is a clinical-stage biopharmaceutical company focused on the development of GP2, an immunotherapy to prevent breast cancer recurrences in patients who have previously undergone surgery. GP2 is a 9 amino acid transmembrane peptide of the HER2 protein, a cell surface receptor protein that is expressed in a variety of common cancers, including expression in 75% of breast cancers at low (1+), intermediate (2+), and high (3+ or over-expressor) levels. Greenwich LifeSciences has commenced a Phase III clinical trial, FLAMINGO-01. For more information on Greenwich LifeSciences, please visit the Company's website at www.greenwichlifesciences.com and follow the Company's Twitter at https://twitter.com/GreenwichLS.

Forward-Looking Statement Disclaimer

Statements in this press release contain "forward-looking statements" that are subject to substantial risks and uncertainties. All statements, other than statements of historical fact, contained in this press release are forward-looking statements. Forward-looking statements contained in this press release may be identified by the use of words such as "anticipate," "believe," "contemplate," "could," "estimate," "expect," "intend," "seek," "may," "might," "plan," "potential," "predict," "project," "target," "aim," "should," "will," "would," or the negative of these words or other similar expressions, although not all forward-looking statements contain these words. Forward-looking statements are based on Greenwich LifeSciences Inc.'s current expectations and are subject to inherent uncertainties, risks and assumptions that are difficult to predict, including statements regarding the intended use of net proceeds from the public offering; consequently, actual results may differ materially from those expressed or implied by such forward-looking statements. Further, certain forward-looking statements are based on assumptions as to future events that may not prove to be accurate. These and other risks and uncertainties are described more fully in the section entitled "Risk Factors" in Greenwich LifeSciences' Annual Report on the most recent Form 10-K for the year ended December 31, 2024, and other periodic reports filed with the Securities and Exchange Commission. Forward-looking statements contained in this announcement are made as of this date, and Greenwich LifeSciences, Inc. undertakes no duty to update such information except as required under applicable law.

Company Contact
Snehal Patel
Investor Relations
Office: (832) 819-3232
Email: info@greenwichlifesciences.com

Investor & Public Relations Contact for Greenwich LifeSciences
Dave Gentry
RedChip Companies Inc.
Office: 1-800-RED CHIP (733 2447)
Email: dave@redchip.com

FAQ

What did Greenwich LifeSciences announce about FLAMINGO-01 on December 15, 2025 (GLSI)?

A preliminary analysis in the open-label non-HLA-A*02 arm (250 patients) suggested an approximately 80% reduction in recurrence rate using two comparison methods.

How was the ≈80% recurrence reduction in GLSI FLAMINGO-01 calculated?

Two methods: comparison to historical T-DM1 (KATHERINE) recurrence rates and within-cohort comparison of 100 patient-years during PIS vs 132 patient-years post-PIS.

Does the GLSI FLAMINGO-01 non-HLA-A*02 arm include a placebo control?

No; the 250-patient non-HLA-A*02 arm is open-label and does not have a direct placebo comparator.

How does the FLAMINGO-01 non-HLA-A*02 result compare to Phase IIb GLSI-100 data?

The open-label observation is trending similarly to Phase IIb, which reported ≈80% reduction in recurrences in HLA-A*02 patients.

What is the follow-up duration behind the reported GLSI FLAMINGO-01 data?

The post-PIS analysis covers 132 patient-years, described as about 9 months average follow-up after PIS completion.

Are these GLSI FLAMINGO-01 results final and predictive of study outcome?

No; the company describes the findings as preliminary, data are not fully reviewed, and results may change as the study matures.