FDA Fast Tracks Vaccine For Some With Breast Cancer

The FDA has granted Fast Track designation to the cancer vaccine GLSI-100 for patients with HLA-A*02-positive and HER2-positive breast cancer.

The U.S. Food and Drug Administration (FDA) has granted fast track designation to the cancer vaccine GLSI-100 for patients with HLA-A*02-positive and HER2-positive breast cancer.

The development, based on findings from the phase 3 FLAMINGO-01 clinical trial evaluating the immunotherapy GLSI-100 to prevent breast cancer recurrences, was announced in a news release issued by clinical-stage biopharmaceutical company Greenwich LifeSciences, Inc.

The designation, according to the news release, states that "GLSI-100 for the treatment of patients with HLA-A*02 genotype and HER2-positive breast cancer who have completed treatment with standard of care HER2/neu targeted therapy to improve invasive breast cancer free survival meets the criteria for fast track designation."

Fast track, as the FDA explains on its website, is a process designed to facilitate the development and expedite the review of drugs to treat serious conditions and fill an unmet medical need.

"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," stated Dr. Jaye Thompson, vice president of clinical and regulatory affairs, in the news release.

CEO Snehal Patel commented in the news release: "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 need. 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. The company plans to continue discussions with the FDA, and potentially the European regulatory authorities, to explore additional ways to make GP2 and GLSI-100 available to larger populations."

Findings from the FLAMINGO-01 trial

Treatment with GLSI-100 has demonstrated an increased immune response over time in patients with HER2-positive breast cancer following surgery, according to preliminary immune response data from the phase 3 FLAMINGO-01 trial, as CURE previously reported.

Data from the trial showed that GLSI-100 is creating an immune response over time, with the treatment creating visible skin reaction at the injection site — a positive sign that a patient’s immune system is responding to treatment. Moreover, patients on both the HLA-A*02 — which is a genetic marker that helps the immune system recognize diseases — and non-HLA-A*02 arms experienced an immune response which increased over time from baseline through the fourth to sixth month.

FLAMINGO-01, the company detailed in the news release, is a phase 3 clinical trial examining the safety and effectiveness of GLSI-100 in patients with HER2-positive breast cancer who had residual disease or high-risk pathologic complete response at surgery and who have completed both neoadjuvant and postoperative adjuvant Herceptin (trastuzumab)-based treatment.

The trial, which is still recruiting participants, plans to eventually enroll 750 patients and is estimated to be completed in December 2026, according to its listing on clinicaltrials.gov.

GLSI-100, as defined by the National Cancer Institute on its website, is a cancer peptide vaccine that contains the epitope GP2, a nine amino acid peptide which may induce a cytotoxic T-lymphocyte (CTL)-mediated immune response against tumor cells expressing the HER2/neu antigen, which may result in the inhibition of proliferation of HER2/neu-expressing tumor cells.

The prospective, randomized, double-blinded, placebo-controlled, multi-center trial involves patients receiving six intradermal injections over the first six months of treatment and then five booster intradermal injections spaced six months apart, the National Cancer Institute explains on its website.

References

1. “Greenwich LifeSciences’ GLSI-100 Granted US FDA Fast Track Designation,” news release, Sept. 10, 2025; https://investor.greenwichlifesciences.com/news-events/press-releases/detail/102/us-fda-fast-track-designation
2. “Fast Track,” FDA; https://www.fda.gov/patients/fast-track-breakthrough-therapy-accelerated-approval-priority-review/fast-track
3. “Investigative Agent Elicits Responses in Phase 3 Breast Cancer Trial,” CURE, April 3, 2025; https://www.curetoday.com/view/investigative-agent-elicits-responses-in-phase-3-breast-cancer-trial
4. “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);’ https://clinicaltrials.gov/study/NCT05232916
5. “HER2/neu peptide vaccine GLSI-100,” National Cancer Institute; https://www.cancer.gov/publications/dictionaries/cancer-drug/def/her2-neu-peptide-vaccine-glsi-100
6. “Phase 3 Study to Evaluate the Efficacy and Safety of HER2/Neu Peptide GLSI-100 (GP2 + GM-CSF) in HER2/Neu Positive Subjects,” National Cancer Institute; https://www.cancer.gov/research/participate/clinical-trials-search/v?id=NCI-2022-03768&r=1

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