A Trial to Evaluate Sacituzumab Govitecan in Combination With Endocrine Therapy in Patients With HR-positive, HER2-negative Metastatic Breast Cancer Progressed on CDK4/6 Inhibitors

SoGreat is an open-label, single-arm, modular, two-stage, Phase Ib/II study. SoGreat (Part 1) is an open-label, modular, Phase Ib study. The study consisted of an up to 28-day Screening period, followed by the Treatment Phase and Follow-up. Screen Period: It is to determine baseline disease characteristics and to confirm patient eligibility prior to randomization and treatment. If tumor evaluation performed as part of routine clinical practice provides valid results within the permitted time frame (within 28 days prior to C1D1), there is no need to repeat tumor imaging at the screening visit. Bone scan (99m technetium polyphosphate scintigraphy, whole body bone MRI, or 18F-NaF/FDG PET) is required to assess bone metastasis within 6 weeks prior to C1D1 (historical scans are acceptable); Eligible patients will be assigned to one of the following 2 treatment modules based on different endocrine agents previously combined with CDK4/6 inhibitors in the advanced first-line setting: Module 1: Fulvestrant 500 mg IM, Days 1 \& 15 of cycle 1 and Day 1 for all other cycles thereafter IF patients progressed on the first-line treatment of CDK4/6i combined with aromatase inhibitors. Module 2: one of the two investigators' choices of aromatase inhibitors (ICAI) oral QD IF patients progressed on the first-line treatment of CDK4/6i combined with Fulvestrant. Mutual substitution is not allowed during the study. Treatment Phase: Sacituzumab Govitecan will be administered in 21-day cycles on Days 1 and 8; the next cycle should start 14 days after the Day 8 dose (i.e., the Day 8 infusion will be counted as the first day of that 14-day period). However, visit windows of 1 day prior to and 2 days after the scheduled infusion are permitted. The scheduled Day 1 and Day 8 infusions may be delayed for up to 3 weeks for treatment-related toxicities. Dose modifications are permitted for sacituzumab govitecan per product inserts (NMPA v2023/03/01). Dose modifications are NOT permitted for endocrine therapy. Treatment was continued until disease progression, unacceptable toxicity, or patient or physician decision. Patients who have experienced a complete response (CR) were to be treated for a minimum of 12 months and/or until disease progression or unacceptable toxicity, after confirmation of response. Tumor measurements by computed tomography (CT) scan or magnetic resonance imaging (MRI; chest, abdomen, pelvis, other areas of known/suspected involvement, with contrast as appropriate) were to be performed every 6 weeks to determine response to treatment, after Week 12, assessments were to be performed every 12 weeks. The response was evaluated using the RECIST v 1.1. Disease progression per RECIST v 1.1 leading to treatment withdrawal was assessed by the Investigator. Clinical progression leading to patient discontinuation was to be documented also by CT/MRI scan, if possible. NCI-CTCAE v 5.0 toxicity grades were used to classify safety evaluations and adverse events, including serious adverse events (SAEs). Adverse event reporting was started after written informed consent was obtained from the patient and continued for 30 days after the last administration of the IP. End of Treatment visit was to be planned within 7 days from the decision to discontinue the investigational product (IP), or before the start of any other antitumor therapy. If the patient discontinues study treatment prematurely without objective progression and initiating any other antitumor therapy, then tumor assessment was to be continued in follow-up visits until progression or death. Follow-Up: A safety Follow-up visit was to be performed 30 days (+/- 3 days) after the last administration of IP. Survival follow-up was to be performed every 12 weeks (+/- 1 week) after the Safety Follow-up visit, might be by telephone, and included the documentation of any further active therapy administrated for their breast cancer. Periodic evaluations of the study data were conducted by a Safety Monitoring Committee (SMC) to ensure patient safety and the validity and scientific merit of the study.