A Phase 3 study on the efficacy and safety of the new HER2/neu peptide GLSI-100 in patients with HER2-positive breast cancer following adjuvant therapy to prevent recurrence

Breast cancer (mammary carcinoma) is a malignant disease of the mammary gland tissue characterized by the uncontrolled proliferation of mammary gland cells. Treatment of the disease depends on numerous factors, such as the patient’s overall health, the stage of the disease, the tumor’s growth rate (Ki-67 index), the presence of detectable hormone receptors on the surface of the cancer cells (estrogen receptor- or progesterone receptor-positive), and the increased expression of the HER2 protein on the cancer cells (HER2-positive).

For HER2-positive breast cancer, drugs are used that specifically recognize and attack breast cancer cells via HER2. These include, for example, trastuzumab, which is already approved. The standard treatment for breast cancer without spread to other parts of the body (metastases) consists of an initial treatment phase (neoadjuvant), surgery on the breast and, if necessary, the lymph nodes, as well as—depending on individual risk—a subsequent treatment phase (adjuvant). For HER2-positive breast cancer, trastuzumab is used as standard treatment in this phase. Nevertheless, there is a risk that the disease will become active again over time (recurrence) despite successful treatment. Therefore, strategies are being sought to reduce this risk. One such strategy could involve training the body’s own immune system to recognize and fight HER2-positive cancer cells when they reappear in the body as a recurrence. The new, not-yet-approved drug HER2/neu peptide GLSI-100 takes precisely this approach. Through repeated doses, similar to a vaccination, the immune system is stimulated to recognize and destroy HER2-positive tumor cells at an early stage.

The goal of the FLAMINGO-01 study is to test whether the therapy can reduce the risk of recurrence compared to a placebo (inactive substance). HER2/neu peptide GLSI-100 is injected into the skin a total of six times over a six-month period and then administered again every six months for an additional 2.5 years (11 times in total). The study is double-blind, meaning that neither the patient nor the medical staff knows whether HER2/neu peptide GLSI-100 is being administered (study arm 1) or the placebo (study arm 2). The study is primarily aimed at patients who have a specific genetic trait (known as HLA-A*02-positive). However, there is also a third study arm in which it is certain that the HER2/neu peptide GLSI-100 will be administered. For this arm, it is essential that patients do not have the HLA-A*02 genetic marker. The study will monitor the recurrence rate over a period of four years.

Women and men aged 18 and older who have stage 1–3 HER2-positive breast cancer are eligible to participate in the study. The breast cancer must not have metastasized. Patients should have already received neoadjuvant and adjuvant treatment with trastuzumab in accordance with standard therapy. Adjuvant therapy must have been completed no more than one year ago. In addition, patients should be in good physical condition and not currently receiving chemotherapy.