Greenwich LifeSciences Provides Update Showing Continued Reduction in Recurrence Rate in the Open Label Arm of FLAMINGO-01

Greenwich LifeSciences (Nasdaq: GLSI) reported a preliminary update from the fully enrolled 250‑patient open label non‑HLA‑A*02 arm of Phase III FLAMINGO‑01.

Rhea-AI Summary

Greenwich LifeSciences (Nasdaq: GLSI) reported a preliminary update from the fully enrolled 250‑patient open label non‑HLA‑A*02 arm of Phase III FLAMINGO‑01. Following completion of the primary immunization series, the observed recurrence rate is <1% per year (0.7% over 1.2 patient‑years), versus ~4% per year in the Katherine study, an ~83% reduction (Chi‑Square p < 0.005). Data are preliminary, based on site reports, and may change as data are cleaned and follow‑up continues.

Most non‑HLA‑A*02 patients completed the six‑month PIS; ~110 patient‑years are added every six months.

Positive

• <1% annual recurrence rate observed in 250 patients
• Approximately 83% reduction versus Katherine (0.7% vs 4%)
• Statistical significance reported: Chi‑Square p < 0.005
• Fully enrolled 250‑patient non‑HLA‑A*02 open label arm
• Majority completed the six‑month primary immunization series

Negative

• Open label arm lacks a direct placebo comparator cohort
• Results are preliminary and based on incomplete site data
• Kaplan‑Meier survival analysis not possible for this arm
• Prior TDM1 treatment and future Enhertu enrollment may confound rates

Argus Mar 17 session

+6.83% close to close Open Argus

Details

News Market Reaction – GLSI

In the Mar 17 session, GLSI gained 6.83%, reflecting a notable positive market reaction.

Data tracked by StockTitan Argus on the day of publication.

Market Context

The stock moved +6.8% in the session following this news. A strong positive reaction aligns with pri...

Analysis

The stock moved +6.8% in the session following this news. A strong positive reaction aligns with prior patterns where GLIS-100 and FLAMINGO‑01 milestones often coincided with sizeable gains, such as moves of 5.65% to 9.62% after earlier updates. The reported <1% annual recurrence rate versus a 4% benchmark and statistically significant p < 0.005 outcome supported enthusiasm. However, the company has previously flagged going-concern risks and relies on ongoing financing, which could temper the durability of sentiment as data mature.

Key Figures

Non-HLA-A*02 arm size: 250 patients Annual recurrence rate: <1% per year Comparator recurrence rate: 4% per year +5 more

Non-HLA-A*02 arm size

250 patients

Fully enrolled open-label non-HLA-A*02 arm of FLAMINGO-01

Annual recurrence rate

<1% per year

Non-HLA-A*02 patients treated with GLSI-100 after PIS

Comparator recurrence rate

4% per year

Kadcyla (TDM1) arm in Katherine study over similar period

Observed annual rate

0.7% vs 4%

Non-HLA-A*02 GLSI-100 patients vs Katherine study over 1.2 years

Exposure duration

1.2 patient-years

Average follow-up for non-HLA-A*02 GLSI-100 patients

Reduction in recurrence

83% reduction

Non-HLA-A*02 GLSI-100 patients vs 4% annual rate benchmark

Statistical significance

p < 0.005

Chi Square test comparing recurrence rates

Data accumulation rate

110 patient-years / 6 months

Non-HLA-A*02 patient database growth in FLAMINGO-01

Historical Context

5 past events · Latest: Mar 16

5 events

1. Mar 16

   Manufacturing update

   24h Move

   +8.4%

   FDA-approved commercial GP2 vials supplied to ~40 US FLAMINGO-01 sites.

2. Mar 03

   Enrollment update

   24h Move

   -0.5%

   Screening rate in FLAMINGO-01 increased to over 800 patients per year.

3. Feb 24

   Conference abstracts

   24h Move

   +9.6%

   Two GLSI-100 abstracts accepted for AACR 2026 presentation.

4. Jan 27

   Financing update

   24h Move

   +9.6%

   ATM sales exceeded ~$9.5M 2025 burn, boosting cash levels.

5. Jan 22

   FDA approval

   24h Move

   +5.7%

   FDA approved use of first commercial GP2 lot in FLAMINGO-01.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Key Terms

open label, kaplan meier, survival analysis, chi square, +4 more

8 terms

open label medical

"preliminary update showing a continued reduction in the recurrence rate in the fully enrolled, 250 patient, open label non-HLA-A*02 arm"

Open label is a clinical trial design in which both the participants and the researchers know which treatment or intervention is being given. For investors, this matters because knowledge of the treatment can influence reported effects and side effects—like how seeing a product label can change a shopper’s opinion—so open-label results are useful for safety and real-world experience but are generally viewed as less rigorous evidence of effectiveness than blinded studies.

kaplan meier medical

"does not have a direct placebo comparator arm, thus a Kaplan Meier survival analysis is not possible"

Kaplan-Meier is a statistical method and chart that shows how long it takes for a defined event (such as recovery, relapse or death) to occur in a group over time while properly handling people who leave the study early. Investors use these curves to assess how long a treatment’s benefits last and how likely it is to succeed in trials—differences in the curves or in median times can signal clinical advantage and potential commercial impact.

survival analysis medical

"does not have a direct placebo comparator arm, thus a Kaplan Meier survival analysis is not possible"

A statistical method that studies how long it takes for a specific event to happen — for example, a patient’s death or recovery, a machine’s failure, a customer leaving, or a loan default. It matters to investors because it turns time-based outcomes into measurable risks and chances of success, much like a stopwatch that compares how quickly different products or treatments reach an endpoint, and thus informs valuation, clinical progress, and risk estimates.

chi square medical

"83% reduction in recurrence rate, Chi Square, p < 0.005"

A chi-square is a statistical measure that compares what actually happened with what would be expected by chance by summing the squared differences between observed and expected counts. Investors use it to test whether patterns in data—such as trading behavior, model predictions, or default rates—are likely real or just random; like checking whether a coin is fair, it helps validate models, detect anomalies, and avoid decisions based on noise.

p < 0.005 medical

"83% reduction in recurrence rate, Chi Square, p < 0.005"

p < 0.005 means a statistical test found that the chance a reported result happened just by random luck is less than 0.5%. Think of it like flipping a coin thousands of times and seeing a pattern so unlikely it would occur fewer than 5 times in 1,000 by accident. For investors, such a low p-value suggests stronger evidence that a drug, strategy, or claim reflects a real effect rather than random noise, but it does not measure how large or practically important that effect is.

phase iib medical

"trending similarly to the Phase IIb trial results and hazard ratio"

Phase IIb is a mid-stage clinical trial that tests whether an experimental treatment works and what dose is best by studying it in a larger group of patients than early tests. For investors, Phase IIb results are important because they substantially reduce uncertainty about a drug’s effectiveness and safety, and positive or negative outcomes often drive company valuation, partnership interest, and the likelihood of advancing to the large, costly Phase III trials.

hazard ratio medical

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

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.

adjuvant setting medical

"if Enhertu is approved for high risk patients in the adjuvant setting, more Enhertu treated patients"

Adjuvant setting describes giving a medical treatment after a main therapy (most often after surgery) to lower the chance that a disease will return; think of it as applying a follow-up guard to catch any remaining cells the primary treatment missed. For investors this matters because success in the adjuvant setting can greatly expand the number of patients eligible for a drug, extend treatment durations, and change regulatory and commercial value compared with use only in later-stage or salvage care.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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STAFFORD, Texas, March 17, 2026 (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 provided a preliminary update showing a continued reduction in the recurrence rate in the fully enrolled, 250 patient, open label non-HLA-A*02 arm of FLAMINGO-01.

• 6 Months of Additional Patient Data Since Last Update Shows Recurrence Rate of <1% per Year in Non-HLA-A*02 Patients Treated with GLSI-100, Following Completion of Primary Immunization Series (PIS)
  
  
• This <1% Annual Recurrence Rate Observed in Non-HLA-A*02 Patients is Statistically Significantly Smaller Than a 4% Annual Recurrence Rate Over a Similar Time Period Observed in the Katherine Study (Kadcyla Treated Arm) Yielding an Approximately 70-80% Reduction in Recurrence Rate as Explained Below
  

The non-HLA-A*02 arm does not have a direct placebo comparator arm, thus a Kaplan Meier survival analysis is not possible, and the following method was used:

• The <1% recurrence rate per year of these 250 treated patients after completing the PIS was compared to the expected historical recurrence rate per year reported for a similar population in the Katherine study who received TDM1 (Kadcyla), which is about 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.
  
  
• As of this data cut, the current recurrence rate of the non-HLA-A*02 patients treated with GLSI-100, following completion of the PIS over an average of 1.2 years of patient exposure, is statistically significantly smaller than a 4% annual recurrence rate over a similar time period observed in the Katherine study (0.7% versus 4% annual recurrence rate over 1.2 patient-years, 83% reduction in recurrence rate, Chi Square, p < 0.005). This preliminary data will continue to be updated and cleaned, so future and final results may vary. Future updates may be presented at upcoming conferences.
  

• 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.
  

Additional information about the non-HLA-A*02 arm follows:

• Virtually all of the non-HLA-A*02 patients have completed the primary immunization series, which is the first 6 monthly vaccinations in the study.
  
  
• Every 6 months approximately 110 patient-years are added to the non-HLA-A*02 patient data base.
  
  
• Enhertu (T-DXd) treated patients can be enrolled in FLAMINGO-01. In the future, if Enhertu is approved for high risk patients in the adjuvant setting, more Enhertu treated patients could be enrolled in FLAMINGO-01 and may recur at a lower rate than if treated with Kadcyla. The recurrence rate assumptions in the design of FLAMINGO-01 include this possibility as well as other potential improvements in standard of care.
  

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 FLAMINGO-01 Open Label Phase III Data

More than 1,000 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 compared to the recurrence rates comparable to those observed in the Katherine study of Kadcyla shows an approximately 70-80% reduction in recurrence rate.
  
• This non-HLA-A*02 arm 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.
  

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 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 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 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

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What recurrence rate did GLSI (Nasdaq: GLSI) report for non‑HLA‑A*02 patients in FLAMINGO‑01 on March 17, 2026?

According to the company, the non‑HLA‑A*02 arm showed a <1% annual recurrence rate (0.7% over 1.2 patient‑years). This preliminary figure is based on 250 fully enrolled patients after completing the primary immunization series and may be updated.

How does the FLAMINGO‑01 non‑HLA‑A*02 recurrence rate compare to the Katherine study for GLSI (GLSI)?

According to the company, the observed rate (~0.7% annually) is ~83% lower than the ~4% annual recurrence reported in the Katherine Kadcyla arm. The comparison produced a Chi‑Square p < 0.005, per the company.

Is the FLAMINGO‑01 non‑HLA‑A*02 result final and peer reviewed for GLSI?

No; according to the company, these results are preliminary and based on site‑reported data that are not fully reviewed or cleaned. Final results may change as data are completed and validated.

Why can't GLSI provide a Kaplan‑Meier analysis for the non‑HLA‑A*02 arm of FLAMINGO‑01?

According to the company, the open label non‑HLA‑A*02 arm has no direct placebo comparator, so a Kaplan‑Meier survival analysis is not possible for that cohort. The team used historical Katherine study rates instead.

How much additional exposure will FLAMINGO‑01 non‑HLA‑A*02 patients add over time for GLSI?

According to the company, approximately 110 patient‑years are added to the non‑HLA‑A*02 dataset every six months as follow‑up continues. Ongoing accrual of exposure may change recurrence estimates over time.