A Phase I, Multicenter, Open-Label, Multi-Part, Dose-escalation Study of RAD1901 in Postmenopausal Women With Advanced Estrogen Receptor Positive and HER2-Negative Breast Cancer

The primary objective is to determine the maximum tolerated dose (MTD) and/or recommended Phase 2 dose (RP2D) of elacestrant in patients with advanced ER+HER2-negative breast cancer.

The secondary objectives of this study are:

• To assess the safety and tolerability of elacestrant
• To evaluate the pharmacokinetics (PK) of elacestrant
• To evaluate the preliminary anti-tumor effect of elacestrant

Key Inclusion Criteria:

• Patients must be post-menopausal women, as defined in the protocol
• 18 years or older
• Patients with histological or cytological proven diagnosis of adenocarcinoma of the breast with evidence of either locally advanced, inoperable and/or metastatic disease
• Part A, B, C: Patients must have received no more than 2 prior chemotherapeutic regimens and at least 6 months of prior endocrine therapy
• Part D: Patients may have received up to 1 previous line of chemotherapy and must have previously received 2 or more lines of endocrine therapy for advanced/metastatic breast cancer as a single agent or in combination. Patients must have received fulvestrant as one of the previous lines of endocrine therapy and have had documented progression while on, or within 1 month after the end of, fulvestrant therapy for advanced/metastatic breast cancer. Patients must have received prior treatment with a CDK4/6 inhibitor

Note: This list is not complete. Further inclusion criteria is provided in the protocol synopsis.

Key Exclusion Criteria:

• Prior anticancer or investigational drug treatment within the following windows:

• Tamoxifen therapy less than 14 days before first dose of study treatment
• Part A, B and C: Fulvestrant therapy less than 90 days before first dose of study treatment. Part D: Fulvestrant therapy less than 42 days before first dose of study treatment
• Any other anti-cancer endocrine therapy less than 14 days before first dose of study treatment
• Any chemotherapy less than 28 days before first dose of study
• Any investigational drug therapy less than 28 days or 3 half-lives (whichever is longer) prior to first dose of study treatment
• Patients with untreated or symptomatic central nervous system (CNS) metastases
• Patients with endometrial disorders, including evidence of endometrial hyperplasia, dysfunctional uterine bleeding or cysts

Note: This list is not complete. Further exclusion criteria is provided in the protocol synopsis.