Comparison of treatment with the approved study drug elacestrant versus standard antihormonal therapy in patients who have undergone surgery for hormone receptor-positive, HER2-negative, non-metastatic breast cancer

Breast cancer (mammary carcinoma) is a malignant disease of the breast glandular tissue in which cells multiply uncontrollably. Treatment depends on various factors, including the patient’s overall health, tumor stage, growth rate (e.g., Ki-67 index), hormonal receptor status (estrogen/progesterone receptors), and HER2 status. As long as the cancer has not metastasized (spread to other organs), the initial goal is to completely remove it through chemotherapy (usually neoadjuvant) followed by surgery. Depending on the risk of recurrence, this is followed by further treatment (adjuvant), such as anti-hormone therapy for hormone receptor-positive breast cancer. Before menopause, tamoxifen is usually used; after menopause, an aromatase inhibitor is used, either alone or in combination.

The study drug elacestrant is also used for anti-hormone therapy and belongs to the class of selective estrogen receptor degraders (SERDs), which promote the degradation of estrogen receptors and thus inhibit estrogen-dependent tumor growth. The drug is already approved for the treatment of advanced estrogen receptor-positive, HER2-negative breast cancer in patients with a specific genetic mutation whose disease has progressed despite treatment with at least one anti-hormonal therapy.

The goal of this Phase 3 study is to investigate the efficacy and safety of elacestrant therapy compared to standard anti-hormone therapy. As part of the study, patients will be randomly assigned to two groups. Group 1 (study arm) will receive the study drug elacestrant once daily for five years. Group 2 (control arm) receives standard anti-hormone therapy with an aromatase inhibitor or tamoxifen. The study is open-label, meaning that both the medical staff and the patients know which medications are being administered. Treatments as part of the study are administered over a period of up to 5 years, during which the efficacy of the therapy and the occurrence of side effects from the various medications are evaluated. A 4-week follow-up period is included. The primary endpoint of the study is invasive breast cancer-specific disease-free survival (IBCFS), defined as the time from the start of therapy without a recurrence of breast cancer.

Women and men aged 18 and older with newly diagnosed, early-stage, hormone receptor-positive, HER2-negative breast cancer are eligible to participate in this study. The disease must not have metastasized and must have already been treated with surgery followed by anti-hormone therapy for 24–60 months. This treatment must not have been interrupted for more than six months. Patients who have previously received treatment with a CDK4/6 inhibitor or a PARP inhibitor must have either completed or discontinued that treatment.