Sacituzumab Govitecan and Q901 in Advanced TNBC

1. Study design: A multicenter, open-label, single-arm Phase II study conducted at six institutions in Korea. This is a multicenter, open-label, single-arm phase II clinical trial designed to evaluate the efficacy and safety of Sacituzumab govitecan (SG) in combination with Q901 in patients with advanced (metastatic/recurrent/unresectable) triple-negative breast cancer (TNBC) whose disease has progressed following prior therapy, in the third-line treatment setting. Subjects enrolled in this trial must be patients diagnosed with advanced TNBC who have received at least 2 prior lines of systemic anticancer therapy, which may include chemotherapy, targeted therapy, or immunotherapy. However, for subjects who received adjuvant/neoadjuvant chemotherapy for resectable-stage breast cancer and relapsed within 12 months after completion of the last chemotherapy, the adjuvant/neoadjuvant chemotherapy is counted as one line of therapy. There are no restrictions on the type or sequence of prior therapies, but all subjects must have measurable disease per RECIST 1.1 criteria at the time of enrollment. 2. Study Treatment Arm Subjects will be assigned to a single treatment arm and will receive the following combination regimen: * Sacituzumab govitecan (SG): 10 mg/kg administered intravenously on Day 1 and Day 8 of each 21-day cycle * Q901: 126 mg/m² administered intravenously on Day 1 and Day 8 of each 21-day cycle Each treatment cycle is defined as 21 days, and study drug administration will continue until disease progression, unacceptable toxicity, discontinuation of treatment at the discretion of the investigator or subject, withdrawal of consent, or death. 3. Safety Run-in Phase Prior to full-scale phase II enrollment, this trial includes a safety run-in phase to evaluate the initial safety and dose appropriateness of the SG plus Q901 combination. In the safety run-in phase, a small number of subjects will receive the combination regimen to assess the occurrence of dose-limiting toxicities (DLTs); if DLTs are observed, dose de-escalation of Q901 will be considered. Based on the results of the safety run-in, the final combination dose to be used in the phase II portion will be determined, after which expansion enrollment will proceed. The key items to be assessed during the safety run-in phase are as follows: Occurrence and characteristics of DLTs Frequency and severity of treatment-related adverse events Initial tolerability of the SG plus Q901 combination regimen 4. Principles for Management of Adverse Events If adverse events occur during administration of the combination regimen in this trial, Sacituzumab govitecan (SG) will be dose-reduced, delayed, or discontinued in accordance with the prescribing information and standard clinical guidelines, while Q901 will follow the dose modification and reduction principles established in its phase I clinical trial. When adverse events occur, independent dose reduction or schedule adjustment for the relevant study drug may be applied based on the assessed relationship (attribution) of the event to each drug. 5. Target Number of Subjects and Primary Endpoint The target enrollment for this trial is a total of 36-48 subjects (6-18 in safety run-in + 30 in phase II), which has been set taking the dropout rate into consideration. This trial is designed as a single-arm study, with the Objective Response Rate (ORR) of the combination regimen set as the primary efficacy endpoint. Tumor response will be assessed according to RECIST version 1.1 criteria, with computed tomography (CT) or magnetic resonance imaging (MRI) of the chest, abdomen, and pelvis performed at baseline prior to enrollment and repeated every 8 weeks thereafter until disease progression. Safety will be assessed continuously throughout the study drug administration period, with a defined safety follow-up period conducted after the last dose of study drug.