Announcement • Jun 02
Greenwich LifeSciences, Inc. Presents FLAMINGO-01 Phase III Trial Open Label Data At Asco Annual Meeting 2026
Greenwich LifeSciences, Inc. presented the published abstract and poster from the ASCO Annual Meeting 2026. This is the second abstract and poster presented jointly with the Steering Committee of FLAMINGO-01 with statistically significant injection site reaction (ISR) immune response data, with subgroup analysis by the most prevalent HLA types. In the non-HLA-A02 open label arm where all patients (n=247) were treated with GLSI-100, immune responses to GP2 were measured at baseline and over time using skin tests (DTH) and ISRs. An ISR reaction, erythema (redness) or induration (white hard bump), was used to assess in vivo immune responses in patients. The diameter of the reaction was assessed 48-72 hours after injection but is not reported here. In this preliminary data analysis, there was a significant increase in percentage of patients experiencing an ISR reaction (for both erythema and induration) in vaccination 4, vaccination 5 or vaccination 6 compared to the baseline vaccination. There were 208 patients with both baseline vaccination and vaccination 4, 5 or 6 assessments. Erythema: There was a significant increase in the percentage of patients experiencing erythema ISRs after the 4th, 5th or 6th vaccination compared to the ISRs from the 1st vaccination. In this preliminary analysis, the frequency of ISRs increased significantly from 20.2% of the patients experiencing an ISR after the first vaccination to 55.3% of the patients experiencing an ISR after the 4th, 5th or 6th vaccination (McNemar p < 0.001), representing an increase of 2.7x or 174%. Induration: There was a significant increase in the percentage of patients experiencing induration ISRs after the 4th, 5th or 6th vaccination compared to the ISRs from the 1st vaccination. In this preliminary analysis, the frequency of ISRs increased significantly from 14.9% of the patients experiencing an ISR after the first vaccination to 34.6% of the patients experiencing an ISR after the 4th, 5th or 6th vaccination (McNemar p < 0.001), representing an increase of 2.3x or 132%. As reported in Table 1, each HLA-A type exhibited more frequent immune reactivity with increased GLSI-100 vaccinations with frequency increasing by 60% to 280% over the frequency after the first vaccination. These results are consistent with the GP2 DTH results presented at AACR. Mechanism of Action: A positive immune response is an indicator that the immune system has been activated against recurring cancer cells, potentially leading to the prevention of metastatic breast cancer. The Company previously announced that in the non-HLA-A02 arm, a preliminary analysis of recurrence rates after the Primary Immunization Series (PIS) is completed shows an approximately 70-80% reduction in recurrence rate. Thus, the immune response data is supporting the mechanism of action that reduces recurrences and prevents metastatic breast cancer. This statistically significant non-HLA-A02 open label arm immune response data for both DTH and ISRs is trending similarly to the immune response data in the HLA-A02 patients in the Phase IIb study and the HLA-A02 arms of FLAMINGO-01. The study is ongoing and data collection and cleaning continue, while some patients may still be in their PIS vaccination phase, so final results may vary. The immune response abstract and poster conclusion: The statistically significant increase in the incidence of ISR reactions over time found in this preliminary analysis of GLSI-100 treated non-HLA-A02 patients shows that GLSI-100 treatment should not be limited to HLA-A02 patients. Patients treated with GLSI-100 were increasingly able to mount an immune response to GP2 as evidenced in this preliminary data. Future investigations may explore the use of immune responses to assess correlation of DTH to ISRs, immunogenicity of GLSI-100 by specific HLA type, timing of boosters to sustain immunity, clinical site performance, and the discontinuation of treatment for non-responders. The abstract from immune response data and the members of the Steering Committee follow: Abstract Number: LBA538 - Poster Section 23 on June 1, 2026, 1:30 - 4:30pm CT. Abstract Title: Preliminary injection site reaction immune response results from open-label arm of on-going Phase III study to evaluate the efficacy and safety of GLSI-100 (GP2 + GM-CSF) in breast cancer patients with residual disease or high-risk PCR after both neo-adjuvant and postoperative adjuvant anti-HER2 therapy, Flamingo-01. Background: This Phase III trial is a prospective, randomized, double-blinded, multi-center study (NCT05232916) in HLA-A02 patients at approximately 140 sites in the US and Europe. A third non-randomized arm of approximately 250 non-HLA-A*02 patients is now fully enrolled and preliminary immune response data is presented below. GP2 is a biologic nine amino acid peptide of the HER2/neu protein delivered in combination with Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) that stimulates an immune response targeting HER2/neu expressing cancers, the combination known as GLSI-100. Methods: After standard of care neoadjuvant and adjuvant therapy, 6 intradermal injections of GLSI-100 will be administered over the first 6 months and 5 subsequent boosters will be administered over the next 2.5 years. The participant duration of the trial will be 3 years treatment plus 1 additional year follow-up. Immune responses to GP2 were measured over time using delayed-type-hypersensitivity (DTH) skin tests and injection site reactions (ISRs). The patient population is defined by these key eligibility criteria: 1) HER2/neu positive and HLA, 2) Residual disease or High risk pCR (Stage III at presentation) post neo-adjuvant therapy, 3) Exclude Stage IV, and 4) Completed at least 90% of planned adjuvant trastuzumab-based therapy. Results: All patients (n=247) were vaccinated with GLSI-100. Injection site reactions, erythema (redness) was assessed at various time points and represent an in vivo immune response in patients. The ISR orthogonal mean was measured 48-72 hours following vaccination with GLSI-100. For GP2 treated patients, there was a significant increase in the percentage of patients experiencing ISRs in the 4th, 5th or 6th vaccination compared to the ISRs from the 1st vaccination. In this preliminary analysis, the frequency of ISRs increased significantly from 20.2% of the patients experiencing an ISR after the first vaccination to 55.3% of the patients experiencing an ISR after the 4th, 5th or 6th vaccination (McNemar p < 0.001). The study is ongoing and data collection and cleaning continue so final results may vary.
