AMEERA-6 aims to evaluate the efficacy and tolerability of amcenestrant in comparison with tamoxifen, in patients with hormone receptor-positive (HR+), human epidermal growth factor 2-negative or positive (HER2-/+) breast cancer who were unable to continue their adjuvant aromatase inhibitor therapy due to side effects (treatment-related toxicity).

Adjuvant therapy is given after surgery with or without radiotherapy to help prevent and delay the progression of the disease into a more advanced and incurable form. However, current adjuvant therapies, like aromatase inhibitors, can have side effects for patients, which may cause them to discontinue the medication prematurely. As a result, many of these patients experience disease recurrence.

Amcenestrant is an oral selective estrogen receptor degrader (SERD). This is a type of drug that binds and degrades the estrogen receptor (ER), thereby inhibiting the ER signaling pathway, which is responsible for the proliferation of breast cancer cells sensitive to estrogens.

The purpose of this study is to compare the efficacy of amcenestrant versus tamoxifen and assess tolerance in patients with hormone receptor-positive (HR+), breast cancer who have prematurely ended their adjuvant aromatase inhibitor therapy due to side effects (treatment-related toxicity).

AMEERA-6 is a two-arm study, meaning that patients will be randomly split into two groups (arms) and then the data from these two groups of patients will be compared. Each group will receive a different treatment.

• Arm A: patients will receive amcenestrant and a tamoxifen-matching placebo for 5 years
• Arm B: patients will receive an amcenestrant-matching placebo and tamoxifen for 5 years

The study will last approximately 10 years for participants (5 years of treatment and 5 years of follow up).

The study will enrol 3,738 patients with hormone receptor-positive (HR+) early breast cancer who have discontinued adjuvant aromatase inhibitor therapy due to treatment related side effects (toxicity).

The AMEERA-6 trial is a partnership coordinated by BIG Headquarters in collaboration with the European Organisation for Research and Treatment of Cancer (EORTC) and Alliance Foundation Trials (AFT).

Sanofi is the pharmaceutical partner and sponsor of the study, providing funding and study drugs.

Recruitment opened in January 2022 and was closed as of 17 August (see results section).

650 hospitals and cancer centres in about 29 countries are taking part in the study.

18 BIG member groups are participating in the study.

On 17 August 2022, the sponsor, Sanofi, announced that they will stop the global clinical development programme of amcenestrant and therefore terminate the AMEERA-6 study. This decision follows the recommendation of the Independent Data Monitoring Committee (IDMC) and is based on the outcome of a prespecified interim analysis of the Phase 3 AMEERA-5 trial in advanced breast cancer that showed that amcenestrant in combination with palbociclib did not meet the prespecified boundary for continuation in comparison with the control arm. No new safety signals were observed.

Trial participants will be transitioned to letrozole in combination with palbociclib or another appropriate standard of care therapy, as determined by their physician.

Read Sanofi’s press release dated 17 August.

Not at present.

Sanofi provided funding and drugs for this study, which was run according to BIG’s Principles of Research Conduct.

ClinicalTrials.gov identifier: NCT05128773