BioPharma, Pharma

Sanofi drops out of competitive breast cancer drug race after another trial failure

Sanofi breast cancer drug amcenestrant has failed in a Phase 3 clinical trial, leading the pharmaceutical giant to discontinue all clinical development of the small molecule. The move means Sanofi is out of the competitive chase to develop a so-called “oral SERD” therapy for patients with a certain type of breast cancer.


Sanofi is officially out of the race to develop a breast cancer drug in pill form that could compete against a former blockbuster injectable therapy. The pharmaceutical giant’s contender, amcenestrant, has failed in a pivotal study, a disappointing result that also spells the end for all clinical trials testing the drug.

The decision announced Wednesday follows an interim look at data from the Phase 3 clinical trial. Sanofi said the results did not meet prespecified criteria for continuing, and the independent data monitoring committee recommended stopping the trial. Sanofi said that no new safety signals were reported in the interim results.

Sanofi was developing amcenestrant as a treatment for patients with advanced breast cancer that is estrogen receptor (ER) positive and human epidermal growth factor receptor 2 (HER2) negative. The small molecule is part of a class of drugs called selective estrogen receptor degraders (SERDs). These drugs are intended to degrade the ER receptor that is a key driver of cancer cell growth. The only FDA-approved SERD is AstraZeneca’s fulvestrant. That drug that validated ER degradation as a way to treat cancer, but it’s administered as a painful intramuscular injection and comes with side effects. Fulvestrant’s sales have slipped as it faces generic competition. Big pharma companies and upstart biotechs have been working to develop oral SERDs that could offer better safety and efficacy than injectable SERDS.

The Phase 3 study of amcenestrant was evaluating the drug as a first-line cancer therapy. The drug was tested in combination with Pfizer’s Ibrance, a standard treatment for ER positive/HER2 negative breast cancer. That pairing was compared to treatment with letrozole, which is an older hormone-based cancer treatment, and Ibrance.

The Sanofi drug’s Phase 3 failure follows a Phase 2 miss that tested the drug by itself as a second-line treatment for advanced ER positive/HER2 negative breast cancer. In March, Sanofi reported that this mid-stage study failed to achieve the main goal of improving progression-free survival, which is a measure of how long patients live without the cancer worsening. Amcenestrant was also being tested in a separate Phase 3 study as an adjuvant, a therapy given to keep a treated cancer from coming back. The latest trial failure means that this adjuvant study will also wind down, Sanofi said.

Other companies have stumbled with their oral SERD efforts. In April, Roche reported that its drug, giredestrant, failed to achieve the main goal of improving progression-free survival in patients whose advanced ER positive/HER2 negative breast cancer had advanced despite earlier treatment. According to the Swiss pharmaceutical giant’s financial report for the first half of 2022, that Phase 2 program has been removed from the pipeline but Phase 3 tests of the drug as a first-line treatment and as an adjuvant therapy are ongoing.

With Sanofi bowing out of amcenestrant’s development, partners Menarini Group and Radius Health are frontrunners to commercialize the first oral SERD. The companies reported last fall that their drug, elacestrant, met the main goal of its Phase 3 test. They submitted a new drug application with the FDA in June. Radius was taken private by two private equity companies, a transaction that closed on Monday.

Sanofi said it will continue to review data from its failed amcenestrant study and present the results at some future date. The patients who were being treated with amcenestrant will be transitioned to letrozole in combination with Ibrance or another standard treatment determined by their physicians.

“While we are disappointed by this outcome, our research will further the scientific understanding of endocrine therapies in people with breast cancer,” John Reed, Sanofi’s global head of research and development, said in a prepared statement. “Our sincere gratitude goes to the patients, families and healthcare professionals involved in the amcenestrant clinical development program. Oncology remains a priority area for Sanofi, and we will continue to pursue transformative research to develop new medicines for people living with cancer.”

Public domain image by the National Cancer Institute