Abstract PO4-27-05: A phase I open-label dose escalation trial of FWD1802 as monotherapy and in combination with palbociclib in patients with ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutations

Abstract

Abstract Background: Estrogen receptor (ER) signaling sits at center of the tumor biology in ER+/HER2- breast cancers. Current standard of care involves hormone therapy with agents including selective estrogen receptor modulators (SERMs), selective estrogen receptor degraders (SERDs), and aromatase inhibitors (AIs). Unfortunately, most patients eventually develop resistance to these therapies. Mutations in estrogen receptor 1 (ESR1) are partially responsible for the acquired resistance. Mutated estrogen receptors are still sensitive to fulvestrant but with a much less sensitivity. In January 2023, elacestrant received its first approval for the treatment of postmenopausal women or adult men with breast cancer harboring ESR1 mutations in US. However, there is still great unmet medical need for this population. FWD1802 is a third-generation oral SERD for ER-positive breast cancer patients. It binds competitively to ER, with a much higher affinity than that of fulvestrant. Preclinically, FWD1802 alone and in combination with palbociclib exhibits significant anti-tumor activity in the ER+/HER2- models and in ESR1-mutated models in vitro and in vivo. This ongoing phase I study is to assess the safety, tolerability, pharmacokinetics (PK) and clinical activity of FWD1802 as monotherapy and in combination with palbociclib in ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutations. Methods: This clinical study (CTR20232130) consists of three parts: monotherapy dose escalation (Part A), dose escalation in combination with palbociclib (Part B) and monotherapy dose expansion in ESR1-mutated patients (Part C). A conventional “3+3” design is used for this study. Approximately a total of 129 patients will be enrolled. FWD1802 is administered orally daily. In monotherapy dose escalation study (Part A), at each dose level, a single ascending dose (SAD) is followed by a 28-day continuous multiple ascending dose (MAD) period (defined as 1 cycle). In Part B dose, palbociclib (125 mg daily) is administered on a 28-day treatment cycle with 21-day on treatment and 7-day off treatment, along with the 28-day treatment cycle of FWD1802. The primary objectives include dose limiting toxicity (DLT), maximum tolerated dose (MTD), safety, tolerability, and the recommended phase 2 dose (RP2D) of FWD1802. Secondary objectives include pharmacokinetics characteristics of FWD1802 and its major metabolite as monotherapy and in combination with palbociclib. Preliminary anti-tumor activity including objective response rate (ORR), duration of response (DoR), disease control rate (DCR) and progression-free survival (PFS) will also be evaluated. DLT evaluation will be conducted after the first cycle of multi-dose period, and tumor assessment will be conducted every 8 weeks by investigators according to RECIST version 1.1. Patients with ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutation are eligible for the enrollment. Enrolled patients should have progressed disease, or failed from previous therapy, or intolerable or inaccessible to standard therapy. In addition, patients with ECOG score ≤1 and with adequate renal, cardiac, hepatic, and hematologic function are eligible for enrollment. The monotherapy dose escalation (Part A) is currently ongoing. The dose selection for Part B and Part C will be based on the data from the ongoing Part A. Clinical trial information: CTR20232130. Research Sponsor: Shenzhen Forward Pharmaceuticals Co., Ltd. (FORWARD PHARMA). Citation Format: Ling Zeng, Jin Liu, Dan Wu, Huiwen Ge, Zirui Bian, Chenggang Zhu. A phase I open-label dose escalation trial of FWD1802 as monotherapy and in combination with palbociclib in patients with ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutations [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-27-05.