New breast cancer drug test halted after just 3 patients

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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.