Greenwich LifeSciences Signals Deep Confidence with Insider Lock-up, Positive Trial Data

STAFFORD, Texas – December 29, 2025 – In a dual announcement signaling both long-term corporate commitment and clinical progress, Greenwich LifeSciences, Inc. revealed today that it has extended a share lock-up for its executives and early investors until late 2026. The news was coupled with a highly encouraging preliminary data update from its pivotal Phase III trial for an immunotherapy aimed at preventing breast cancer recurrence.

The clinical-stage biopharmaceutical company (Nasdaq: GLSI) is advancing its lead candidate, GLSI-100, through the FLAMINGO-01 trial. The combination of a significant financial constraint on insiders and positive early-stage results offers a potent message to investors and the medical community about the company's belief in its long-term strategy and the potential of its flagship immunotherapy.

An Unprecedented Six-Year Commitment

In a move rarely seen in the volatile biotech sector, Greenwich LifeSciences' Board of Directors has extended the lock-up agreement for shares held by its directors, officers, and pre-IPO investors to September 30, 2026. This decision effectively prevents insiders from selling their common stock for a total of approximately 72 months, or six years, from the company's initial public offering.

Such a prolonged lock-up period is a powerful statement of internal confidence. Typically, insider lock-ups expire within 180 days post-IPO, allowing early backers and executives to liquidate a portion of their holdings. By extending this period for years, the company's leadership is directly aligning its financial interests with those of its public, long-term shareholders who are betting on the success of the FLAMINGO-01 trial.

CEO Snehal Patel commented on the strategic decision, stating, "This unprecedented 6 years lock-up is controlled by the Board and is designed to align the locked-up shareholders with the Company’s long term investors and to support the FLAMINGO-01 Phase III trial."

Patel also detailed the Board's future flexibility, noting that it could modify the plan based on trial progress or strategic opportunities. The Board has the option to implement a "leak-out plan" or a "10b5-1 trading plan" after the lock-up expires, which would allow for the controlled and organized selling of a predetermined percentage of shares over time. This structured approach is designed to prevent market disruption while still providing eventual liquidity for the locked-up shareholders. Any significant event, such as an interim data analysis or a potential partnership, could also influence the Board's decisions regarding the lock-up's terms.

Promising Early Data from Breast Cancer Trial

Beyond the financial news, Greenwich LifeSciences provided a substantive update on its FLAMINGO-01 Phase III study, which is evaluating GLSI-100, an immunotherapy granted Fast Track designation by the FDA. The company shared promising preliminary data from the trial's open-label arm, which includes 250 non-HLA-A*02 patients who have all received the treatment.

According to the company, a preliminary analysis of this group reveals an approximately 80% reduction in the breast cancer recurrence rate for patients who have completed the initial six-month treatment course, known as the Primary Immunization Series (PIS). This initial series of six injections is designed to bring the patient's immune response to its peak level of protection.

Crucially, the company noted that this observed trend is tracking similarly to the landmark results of its earlier Phase IIb trial. In that study, which focused on a different patient subtype (HLA-A*02), treatment with GLSI-100 led to an 80% or greater reduction in recurrences over a five-year follow-up period. The consistency between the early Phase III data and the completed Phase IIb trial provides a strong, albeit preliminary, signal that the immunotherapy's effect could be robust across different patient populations.

The company also reported that the immune response and safety profile in the current trial arm are trending similarly to previous studies. While the company carefully noted that the analysis is based on incomplete data and is not predictive of the final study results, the update marks a significant milestone. The full enrollment of this 250-patient arm provides a dataset five times larger than the treated group in the Phase IIb trial, offering a more substantial look at the therapy's performance.

The Science Behind GLSI-100

GLSI-100 is an immunotherapy designed to train the patient's own immune system to recognize and attack cells that express the HER2 protein. HER2 is a receptor protein found on the surface of various cancer cells and is expressed at some level in approximately 75% of all breast cancers. By targeting a 9-amino acid peptide segment of this protein, GLSI-100 aims to prevent stray cancer cells from causing a recurrence after a patient has undergone primary treatments like surgery, chemotherapy, and trastuzumab-based therapies.

The ongoing Phase III trial was built upon the success of a multi-center, placebo-controlled Phase IIb study led by the MD Anderson Cancer Center. In that trial, patients who received GLSI-100 and remained disease-free for the first six months—the time needed to achieve peak immunity—saw a dramatic reduction in metastatic breast cancer recurrences over five years. The treatment was also found to be well-tolerated, a critical factor for a preventative therapy administered to patients who are otherwise in remission.

The goal of such an immunotherapy is to provide a durable, long-term surveillance system within the body that can eliminate residual cancer cells before they can develop into recurrent tumors, a devastating outcome for breast cancer survivors.

The Road Ahead for FLAMINGO-01

The FLAMINGO-01 trial is a large-scale, global effort led by Baylor College of Medicine, with plans to operate up to 150 clinical sites across the US and Europe. The study is enrolling HER2-positive breast cancer patients who are at high risk of recurrence, specifically those with residual disease after surgery or a high-risk pathologic complete response.

The trial's main component consists of two double-blinded arms, where approximately 500 patients with the HLA-A*02 genetic profile will be randomized to receive either GLSI-100 or a placebo. The open-label arm, from which the latest data was reported, includes up to 250 patients with other HLA types.

The trial's primary endpoint is invasive breast cancer-free survival. It has been designed with enough statistical power to detect a significant difference between the treatment and placebo groups, with a planned interim analysis for superiority or futility after just 14 recurrence events have occurred. This design allows the company and regulators to get an early look at the data to determine if the trial should continue as planned.

With the combination of a leadership team financially locked in for the long haul and accumulating clinical data that continues to point towards a powerful anti-recurrence effect, Greenwich LifeSciences has positioned itself at a critical juncture in the development of a potentially new standard of care for breast cancer survivors.