Study of Amcenestrant (SAR439859) Versus Tamoxifen for Patients With Hormone Receptor-positive (HR+) Early Breast Cancer, Who Have Discontinued Adjuvant Aromatase Inhibitor Therapy Due to Treatment-related Toxicity

Inclusion Criteria:

Adult participants with histologically confirmed diagnosis of adenocarcinoma of the breast with documentation of hormone receptor-positive status, irrespective of human epidermal growth factor receptor 2 (HER2) status NOTE: Participants with HER2-positive breast cancer were eligible only if they had completed their adjuvant anti-HER2 treatment and chemotherapy.
With Stage IIB or Stage III (invasive breast cancer) who had undergone breast surgery and adjuvant radiation (if indicated) for the current malignancy.
Who had received prior aromatase inhibitors (AIs) (letrozole, anastrozole or exemestane or any sequence thereof) per the following:

Adjuvant AI therapy was discontinued due to AI treatment-related toxicity; Minimum of 6 months duration and maximum of 30 months duration (from initiation of first AI if there was a switch between AIs) of AI therapy was required.

Absence of locoregional and/or advanced/metastatic disease
Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-1
Capable of giving signed informed consent.

Exclusion Criteria:

Medical history or ongoing gastrointestinal disorders potentially affecting the absorption of amcenestrant and/or tamoxifen. Participants unable to swallow normally or unable to take tablets and capsules. Predictable poor compliance to oral treatment. Active inflammatory bowel disease or chronic diarrhea, active hepatitis A/B/C, hepatic cirrhosis, short bowel syndrome, or any upper gastrointestinal surgery including gastric resection or banding procedures.
History of prior breast cancer treated with AI.
Any other solid tumor or lymphoma diagnosis was not allowed except if the participant had been free from disease for equal to greater than (=>5) years.
Pregnant or nursing women, or women of child-bearing potential without a negative pregnancy test prior to randomization.
Participants with unrecovered acute toxic effects of prior AI therapy or surgical procedures.
Uncontrolled intercurrent illness, including psychiatric conditions that would have limited compliance with study requirements.
Treatment with any selective estrogen receptor degrader (SERD), tamoxifen or toremifene were not allowed as prior adjuvant therapy but could have been used as neoadjuvant therapy for a total duration of 3 months. Participants who were treated with a SERD, tamoxifen or toremifene in the neoadjuvant setting and who experienced disease progression were not allowed. Prior treatment with raloxifene or tamoxifen for bone health, risk reduction, or a prior breast cancer was allowed provided this was discontinued at least 3 years before diagnosis of current breast cancer.
Ongoing treatment with HER2 directed therapy. Appropriate wash out between the last dose of HER2 directed therapy and randomization should have been at least 4 weeks.

The above information was not intended to contain all considerations relevant to a potential participation in a clinical trial.