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An open-label, randomized, phase 2 trial of SAR439859, versus endocrine monotherapy as per physician's choice in premenopausal and postmenopausal patients with estrogen receptor-positive, HER2-negative locally advanced or metastatic breast cancer with prior exposure to hormonal therapies (ACT16105)


The purpose of this study is to evaluate the activity of SAR439859, a potent, orally bioavailable, and selective estrogen receptor (ER) inhibitor that belongs to the selective estrogen receptor degrader (SERD) class of compounds in comparison with other endocrine treatments approved for the treatment of breast cancer, including fulvestrant, selective ER modulators (tamoxifen), and AIs (anastrozole, exemestane, and letrozole).


Accepting new patients

Primary Study Objective(s)

The primary objective of this study is to determine whether SAR439859 improves progression free survival (PFS) when compared with an endocrine monotherapy of the choice of the physician, in participants with metastatic or locally advanced breast cancer.

Core eligibility

Note: This is only a partial list of eligibility criteria.

Including patients who meet the following criteria:

  • 18 years or older
  • Histological or cytological diagnosis of adenocarcinoma of the breast
  • Locally advanced not amenable to radiation therapy or surgery in a curative intent, and/or metastatic disease
  • ER positive status
  • HER2 negative status
  • For patients with tumor accessible for paired biopsy at study entry: baseline samples, formalin fixed paraffin embedded (FFPE) archived biopsy samples (within 3 months prior initiation of study treatment) can be used, but preferably fresh biopsies from primary tumor or recurrence or metastasis, will be collected
  • Participants must have received no more than 1 prior chemotherapeutic or 1 targeted therapy regimen for advanced/metastatic disease
  • Participants must have progressed after at least 6 months of a continuous prior endocrine therapy for advanced breast cancer
  • Participants must be postmenopausal women

Excluding patients who meet the following criteria:

  • Eastern Cooperative Oncology Group performance status ≥2
  • Medical history or ongoing gastrointestinal disorders potentially affecting the absorption of SAR439859. Participants unable to swallow normally and to take capsules
  • Participant with any other cancer. Adequately treated basal cell or squamous cell skin cancer or in situ cervical cancer or any other cancer from which the participant has been disease free for >3 years are allowed
  • Severe uncontrolled systemic disease at screening
  • Participants with bone-only metastasis
  • Participants with known brain metastases that are untreated, symptomatic or require therapy to control symptoms
  • Prior treatment with mammalian target of rapamycin inhibitors or any other selective estrogen receptor degrader (SERD) compound, except fulvestrant if stopped for at least 3 months before randomization
  • Treatment with antiviral agents, antifungal, and antioxidant agents less than 2 weeks before randomization
  • Treatment with strong or moderate CYP3A inducers within 2 weeks before randomization.
  • Ongoing treatment with drugs that are substrate of P-glycoprotein (P-gp) (dabigatran, digoxin, fexofenadine)
  • Treatment with anticancer agents (including investigational drugs) less than 3 weeks before randomization
  • Inadequate hematological, coagulation, renal and liver functions

Accepting new patients


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Principal Investigator(s)

Sramila Aithal
Sagun Shrestha