GLSI-100 Gets FDA Fast Track Designation for Breast Cancer

The FDA has granted fast track designation to GLSI-100 for patients with HER2-positive breast cancer with an HLA-A*02 genotype.¹

What Does FDA Fast Track Designation Offer?

Fast track designation is intended to facilitate the development and expedite the review of drugs that fill unmet medical needs.² With this designation, Greenwich LifeSciences, the sponsor, is eligible for more frequent meetings with the FDA, accelerated approval and priority review, and rolling review for a biologics license application (BLA).

"We are excited to have received fast track designation. The FDA review of our fast track application included a review of the potential of GLSI-100 as a new drug to treat serious conditions and to fill unmet medical needs. By showing the potential of GLSI-100 to prevent metastatic breast cancer recurrence in the patient population that we are studying, we were able to estimate the potential lives that could be saved,” said Snehal Patel, CEO of Greenwich LifeSciences, in a press release.¹

"Greenwich is pleased that the FDA sees the potential of GLSI-100 to change important clinical outcomes in this population of breast cancer patients. We continue to work earnestly to collect data to support a BLA filing demonstrating this benefit,” added Jaye Thompson, MD, vice president of Clinical and Regulatory Affairs, in the press release.

What Study Is Evaluating GLSI-100?

GLSI-100 is being evaluated in a phase 3 clinical trial, FLAMINGO-01 (NCT05232916).³ The study is recruiting patients across 159 global sites and is randomizing them to receive GLSI-100 or placebo. The primary end point is invasive breast cancer-free survival, and secondary end points include invasive disease-free survival, distant disease-free survival, overall survival, and quality of life.

To be eligible for study participation, patients are required to have completed both neoadjuvant and adjuvant trastuzumab (Herceptin)-based standard-of-care breast cancer therapy, have an ECOG performance status of 0 to 2, have adequate organ function, and have no clinical evidence of residual or persistent breast cancer per treating physician assessment. Those with stage IV or metastatic breast cancer at any time, inflammatory breast cancer, a history of immunodeficiency, an active autoimmune disease, or an active infection are not eligible for enrollment.

What Is GLSI-100?

GLSI-100 is a potential first-in-class therapy combining GP2, a HER2/neu-derived peptide, with granulocyte macrophage colony-stimulating factor (GM-CSF).⁴ Data from the phase 2b study conducted at MD Anderson Cancer Center and presented at the San Antonio Breast Cancer Symposium in 2020 showed that the agent led to an 80% or greater reduction in metastatic breast cancer recurrence rate over 5 years compared with 20 to 50% in other approved agents. A peak immune response was observed at 6 months as measured using the Dimer Binding Assay and delayed-type hypersensitivity skin test.

The agent had a tolerable safety profile with no reported serious adverse events (AEs) related to treatment.The majority of reported AEs were injection site reactions such as erythema, pruritus, and induration, which were generally of mild severity and similar in incidence between the GLSI-100 and placebo groups.

REFERENCES:

1. Greenwich LifeSciences’ GLSI-100 Granted US FDA Fast Track Designation. News release. Greenwich LifeSciences. September 10, 2025. Accessed September 10, 2025. https://tinyurl.com/3s7nf6dt

2. Fast Track. US FDA. Updated August 13, 2024. Accessed September 10, 2025. https://tinyurl.com/y748ywj9

3. Phase 3 Study to Evaluate the Efficacy and Safety of HER2/​Neu Peptide GLSI-100 (GP2 + GM-CSF) in HER2/​Neu Positive Subjects (FLAMINGO-01). ClinicalTrial.gov. Updated August 26, 2025. Accessed September 10, 2025. https://clinicaltrials.gov/study/NCT05232916

4. Clinical Trials. Greenwich LifeSciences. Accessed September 10, 2025. https://tinyurl.com/5cbyy5nw