Greenwich LifeSciences, Inc. (Nasdaq: GLSI), a clinical-stage biopharmaceutical company, has announced a major regulatory milestone: GLSI-100 receives FDA Fast Track designation. This investigational breast cancer immunotherapy is being developed to prevent recurrence in HLA-A*02 genotype patients with HER2-positive breast cancer who have completed standard HER2-targeted therapy. The designation directly supports the company’s ongoing Phase III trial, FLAMINGO-01, which is evaluating the ability of GLSI-100 to prevent invasive breast cancer recurrence in high-risk patients.
What Does the Fast Track Designation Mean?
According to the FDA, the Fast Track program is intended to accelerate the development and review of drugs that treat serious conditions and fill an unmet medical need. It allows for more frequent interactions with the FDA, eligibility for Accelerated Approval and Priority Review, and importantly, rolling review of the Biologic License Application (BLA).
Greenwich LifeSciences may now submit completed sections of its BLA for GLSI-100 as they become available—rather than waiting for the full application to be finalized—potentially shortening the path to approval.
Dr. Jaye Thompson, VP of Clinical and Regulatory Affairs at Greenwich LifeSciences, emphasized the importance of this development:
“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.”
GLSI-100 and the FLAMINGO-01 Phase III Trial
GLSI-100 is a therapeutic immunization composed of GP2, a HER2-derived peptide, combined with granulocyte-macrophage colony-stimulating factor (GM-CSF). The treatment is designed to stimulate the immune system to target residual cancer cells following surgery and HER2-directed therapies.
The FLAMINGO-01 trial (NCT05232916) is currently enrolling across U.S. and European academic centers, with plans to open up to 150 global sites. The trial includes approximately 500 randomized HLA-A*02 patients and 250 patients of other HLA types. It is powered to detect a hazard ratio of 0.3 in invasive breast cancer-free survival, with interim analysis planned after 14 events.
Snehal Patel, CEO of Greenwich LifeSciences, commented:
“We are excited to have received Fast Track designation. The FDA’s review recognized the potential of GLSI-100 to prevent metastatic breast cancer recurrence. This opens the door to further collaboration with regulatory authorities in the U.S. and potentially in Europe as well.”
Promising Phase IIb Data
In a prior Phase IIb trial led by MD Anderson Cancer Center, 46 HER2-positive HLA-A*02 patients treated with GLSI-100 demonstrated an 80% or greater reduction in breast cancer recurrence over 5 years compared to the placebo group. Notably, the peak immune response was observed at six months, and the treatment showed an excellent safety profile with no serious adverse events.
Booster injections every six months sustained immune activity, and overall, GLSI-100 was well tolerated in over 146 patients across Phase I and II studies.
Why HLA-A*02 Matters
The HLA-A*02 genotype is one of the most common HLA types among breast cancer patients. By targeting this population, GLSI-100 is tailored to a genetically defined subgroup with a high unmet need for recurrence prevention. HER2-positive breast cancer remains a significant concern due to its aggressive nature, despite the availability of approved HER2-targeted therapies like trastuzumab and pertuzumab.
According to recent data, approximately 300,000 new breast cancer cases are diagnosed annually in the United States, with HER2/neu protein expressed in about 75% of cases at varying levels (1+, 2+, or 3+).
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Next Steps for GLSI-100
The Fast Track designation now enables Greenwich LifeSciences to engage in frequent meetings and communication with the FDA, refining their regulatory pathway as they move toward BLA submission. If the FLAMINGO-01 trial confirms the findings from the Phase IIb study, GLSI-100 could become the first therapeutic breast cancer vaccine approved specifically for recurrence prevention in a post-treatment setting.
As the company continues enrollment and data collection, it also plans to explore regulatory opportunities in Europe and potentially expand GLSI-100 access to broader HLA populations in future trials.
For more details or to follow trial updates, visit clinicaltrials.gov\
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Written by Armen Gevorgyan, MD