GLSI-100 Granted Fast Track Designation for HER2-Positive Breast Cancer

GLSI-100 (Greenwich LifeSciences) received a fast track designation from the FDA for the prevention of breast cancer recurrence in patients with HER2-positive (HER2+) breast cancer expressing the HLA-A*02 genotype who completed standard of care HER2-targeted therapy. The decision is based on statistically significant data from the phase 3 FLAMINGO-01 trial (NCT05232916).¹

Microscopic visualization of breast cancer cells | Image Credit: © seoashi - stock.adobe.com

"We are excited to have received fast track designation,” Snehal Patel, chief executive officer of Greenwich LifeSciences. “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.”²

GLSI-100 is an immunotherapy designed to prevent recurrence of breast cancer that demonstrated meaningful efficacy and safety across multiple clinical trials. In a prospective, randomized, single-blinded, placebo-controlled, multicenter, phase 2b trial, patients treated with GLSI-100 achieved an 80% or greater reduction in cancer recurrence after 5 years of follow-up. Additionally, the investigators reported no serious adverse events and a well-tolerated safety profile.²

Emerging data from another trial, FLAMINGO-01, continue to support GLSI-100’s efficacy in this treatment setting. FLAMINGO-01 is a prospective, randomized, double-blinded, placebo-controlled, multi-center, phase 3 study of GLSI-100 immunotherapy in patients with HLA-A*02-positive and HER2+ at high risk for disease recurrence and who have completed both neoadjuvant and postoperative adjuvant standard of care therapy. The trial includes approximately 500 patients with HLA-A*02 who will be randomized to GLSI-100 or placebo, and up to 250 patients of other HLA types who will be treated with GLSI-100 in a third arm.^1,2

The course of treatment includes 5 booster intradermal injections spaced six months apart, as well as six intradermal injections during the first 6 months of the Primary Immunization Series. GLSI-100 immunotherapy will be investigated in a third open-label arm in patients who are HER2+ and non-HLA-A*02-positive.¹

The primary end point is invasive breast cancer-free survival (IBCFS), defined as the time from the first dose of study medication until the date of ipsilateral invasive breast cancer recurrence, ipsilateral local-regional invasive breast cancer recurrence, distant recurrence, contralateral invasive breast cancer, or any cause mortality. Secondary end points include invasive disease-free survival, distant disease-free survival, overall survival, and quality of life.¹

According to the official designation, "GLSI-100 for the treatment of patients with HLA-A*02 genotype and HER2+ breast cancer who have completed treatment with standard of care HER2+ targeted therapy to improve [IBCFS] meets the criteria for fast track designation."²

REFERENCES

1. 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). Clinicaltrials.gov. Updated August 26, 2025. Accessed September 11, 2025. https://www.clinicaltrials.gov/study/NCT05232916

2. Greenwich LifeSciences’ GLSI-100 granted US FDA fast track designation. Greenwich LifeSciences. September 10, 2025. Accessed September 11, 2025. https://investor.greenwichlifesciences.com/news-events/press-releases/detail/102/us-fda-fast-track-designation