News|Articles|March 17, 2026

New Data Show Immunotherapy Reduces Breast Cancer Recurrence by Over 80%

Fact checked by: Alex Biese

Listen

0:00 / 0:00

Key Takeaways

Updated follow-up in the fully enrolled non–HLA-A*02 cohort showed 0.7% recurrence over a mean 1.2 patient-years after the primary immunization series, corresponding to <1% annual recurrence.
Benchmarking against KATHERINE historical data (~4% annual recurrence on ado-trastuzumab emtansine) suggested an 83% reduction, though the comparison is limited by the open-label, nonrandomized design.
GLSI-100 combines GP2 with GM-CSF and is administered as six monthly injections to peak immunity, followed by five boosters every six months to sustain immune protection.
Early safety and immunogenicity trends aligned with prior HLA-A*02 cohorts and phase 2b experience, with increasing immune responses measured by skin testing and immunologic assays, pending data cleaning and review.

A phase 3 trial update for GLSI-100 shows a recurrence rate of less than 1% per year in patients with HER2-positive breast cancer after immunization.

Patients with HER2-positive breast cancer in the FLAMINGO-01 phase 3 clinical trial are seeing a continued reduction in recurrence rates, Greenwich LifeSciences, Inc. has reported.

The preliminary update focused on 250 patients with cancer in the non-HLA-A*02 arm of the study, who are receiving the immunotherapy GLSI-100 to prevent the disease from returning after surgery and standard treatments.

Main data that support the findings

The latest data cut shows a recurrence rate of less than 1% per year in the 250 patients who have completed the primary immunization series. This update includes six months of additional data since the previous report.

Because the non-HLA-A*02 arm is open label and does not have a direct placebo group, researchers compared the results to historical data from the Katherine study. In that study, patients with cancer treated with Kadcyla (ado-trastuzumab emtansine) experienced an annual recurrence rate of approximately 4% or higher. The majority of patients in the current FLAMINGO-01 trial also received Kadcyla followed by the immunotherapy GLSI-100.

The analysis revealed that the current recurrence rate for treated patients is 0.7% over an average of 1.2 patient-years. This is statistically significantly smaller than the 4% annual rate observed in the Katherine study over a similar period, representing an 83% reduction in the recurrence rate. These observations trend similarly to phase 2b trial results, where breast cancer recurrences were reduced by up to 80% in HLA-A*02 patients.

While other approved products have shown a 20% to 50% reduction in recurrence rates, the data for GLSI-100 suggests a reduction of approximately 70% to 80% compared to historical rates. Researchers noted that these results are preliminary and future updates may vary as data is cleaned and reviewed.

Trial details

FLAMINGO-01 is a phase 3 clinical trial evaluating the safety and efficacy of GLSI-100, which consists of GP2 and GM-CSF. The study focuses on patients with HER2-positive breast cancer who have completed Kadcyla-based treatment and had residual disease or high-risk pathologic complete response at the time of surgery.

The trial is led by Baylor College of Medicine and includes university-based hospitals and academic networks in the U.S. and Europe, with plans to open 150 sites globally. The study structure includes:

Approximately 500 HLA-A*02 patients randomized to GLSI-100 or placebo.
Up to 250 patients of other HLA types (the non-HLA-A*02 arm) treated with GLSI-100.

The 250-patient arm is now fully enrolled, which provides five times more data than the approximately 50 patients treated in the previous phase 2b trial. Patients receive a Primary Immunization Series (PIS), consisting of six monthly injections, which is the time required to reach peak immunity. This is followed by five booster injections given every six months to provide longer-term protection.

Safety

The safety profile of patients in the non-HLA-A*02 arm is trending similarly to the HLA-A*02 arms of the trial and the earlier phase 2b study. In that previous study, GLSI-100 demonstrated a well-tolerated safety profile over five years of follow-up.

Patients in the current trial show an increasing immune response during the six-month primary immunization series, similar to the potent immune response measured in the phase 2b study. This response is measured through local skin tests and immunological assays.

While the immune response and safety data currently trend positively, the findings are based on preliminary data provided by clinical sites. This data has not been fully reviewed or completed, and the results at the end of the study may differ from these early observations.

Reference:

“Greenwich LifeSciences Provides Update Showing Continued Reduction in Recurrence Rate in the Open Label Arm of FLAMINGO-01,” news release; https://sg.finance.yahoo.com/news/greenwich-lifesciences-provides-showing-continued-100000670.html

Editor's note: This article is for informational purposes only and is not a substitute for professional medical advice, as your own experience will be unique. Use this article to guide discussions with your oncologist. Content was generated with AI, reviewed by a human editor, but not independently verified by a medical professional.

For more news on cancer updates, research and education, don’t forget to subscribe to CURE®’s newsletters here.