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Evaluating GLSI-100 immunotherapy for HER2 positive breast cancer

A Randomized, Multicenter, Placebo-controlled, Phase 3 Study to Evaluate the Efficacy and Safety of HER2/Neu Peptide GLSI-100 (GP2 + GM-CSF) in HER2/Neu Positive Subjects With Residual Disease or High-Risk PCR After Both Neoadjuvant and Postoperative Adjuvant Trastuzumab-based Therapy (FLAMINGO-01)

PHASE3 · Greenwich LifeSciences, Inc. · NCT05232916

This study is testing a new immunotherapy called GLSI-100 to see if it can help prevent breast cancer from coming back in patients who are at high risk and have HER2 positive breast cancer.

Quick facts

PhasePHASE3
Study typeInterventional
Enrollment750 (estimated)
Ages18 Years to 100 Years
SexAll
SponsorGreenwich LifeSciences, Inc. (industry)
Drugs / interventionstrastuzumab, chemotherapy, immunotherapy
Locations166 sites (Goodyear, Arizona and 165 other locations)
Trial IDNCT05232916 on ClinicalTrials.gov

What this trial studies

This Phase 3 study investigates the efficacy and safety of GLSI-100, an immunotherapy, in patients with HER2/neu positive breast cancer who are at high risk for recurrence. Participants will receive a series of intradermal injections of GLSI-100 or a placebo after completing standard neoadjuvant and adjuvant therapies. The study includes a randomized, double-blinded, placebo-controlled design and also features an open-label arm for non-HLA-A*02 positive subjects. The goal is to assess the treatment's impact on disease recurrence in this high-risk population.

Who should consider this trial

Good fit: Ideal candidates are HLA-A*02 positive individuals with a confirmed diagnosis of HER2/neu positive breast cancer who have completed standard therapies and have residual disease.

Not a fit: Patients without HER2/neu positive breast cancer or those who do not meet the HLA-A*02 positive criteria may not benefit from this study.

Why it matters

Potential benefit: If successful, this treatment could significantly reduce the risk of breast cancer recurrence in patients with HER2/neu positive tumors.

How similar studies have performed: Other studies have shown promise with immunotherapy approaches in similar patient populations, indicating potential for success in this novel application.

Eligibility criteria

Show full inclusion / exclusion criteria 
Inclusion Criteria:

* HLA-A\*02-positive, unless being enrolled in the third non-HLA-A\*02 arm
* Histologically confirmed diagnosis of HER2/neu positive primary breast cancer for all tumors biopsied (multifocal, multicentric, or synchronous contralateral disease)
* Completion of both neoadjuvant and adjuvant trastuzumab-based standard of care breast cancer therapy
* Stage I, II, or III at presentation with pathologic evidence of residual invasive carcinoma in the breast or axillary lymph nodes (residual disease) at surgery following completion of neoadjuvant therapy -OR- Stage III at presentation with pathologic complete response (pCR) at surgery following completion of neoadjuvant therapy
* The subject can begin study therapy within one year of completion of adjuvant trastuzumab-based therapy and any other standard therapies, but, study therapy can be administered concurrently with endocrine therapy.
* No clinical evidence of residual or persistent breast cancer per treating physician assessment
* ECOG 0-2
* Adequate organ function
* Negative pregnancy test or evidence of post-menopausal status
* If of childbearing potential, willing to use a form of highly effective contraception
* Subject must both reside in and have been treated for their cancer in the country in which the clinical site is located.

Exclusion Criteria:

* Stage IV cancer or metastatic breast cancer at any time
* Inflammatory breast cancer
* Receiving other investigational agents
* Receiving chemotherapy
* Requiring long-term systemic treatment with corticosteroids or other immunosuppressive therapy
* History of immunodeficiency or active autoimmune disease
* A history of serious allergic reactions, including anaphylaxis, to human granulocyte-macrophage colony-stimulating factors such as sargramostim, yeast-derived products, or any component of the investigational product
* Other malignancies except adequately treated in situ carcinoma of the cervix or basal cell or squamous cell carcinoma of the skin
* Active infection
* Known HIV infection with a detectable viral load within 6 months of the anticipated start of treatment. Note: Subjects on effective antiretroviral therapy with an undetectable viral load within 6 months of the anticipated start of treatment are eligible for this trial.

Where this trial is running

Goodyear, Arizona and 165 other locations

+116 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.

View on ClinicalTrials.gov →

Conditions: Breast Cancer, HER2/neu positive, Residual disease, pCR, Extended adjuvant, GP2, Immunotherapy, HLA type

Last reviewed 2026-05-15 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.