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Background: Patients (pts) with metastatic triple-negative breast cancer (mTNBC) who have brain metastases represent a poor prognosis cohort with a high unmet clinical need. Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2 antibody coupled to SN-38, an active metabolite of irinotecan, via a unique hydrolyzable linker that allows for SN-38 release intracellularly and in the tumor microenvironment (bystander effect). SN-38 can cross the blood-brain barrier and is a drug partner in central nervous system (CNS) disease regimens (PMID: 18784279; PMID: 26080460). Although antibody-based therapy raises concerns regarding CNS penetration, activity with SG has been seen in intracranial xenograft models (Brenner Neurooncol Adv 2019). In a subgroup analysis from ASCENT, the efficacy and safety of SG were evaluated in pts with stable brain metastases. Methods: In the phase 3 ASCENT study (NCT02574455), 529 pts with mTNBC refractory to or relapsing after at least 2 prior chemotherapies were randomized 1:1 to receive SG (10 mg/kg IV on days 1 and 8 every 21 days) or single-agent treatment of physician’s choice (TPC; capecitabine, eribulin, vinorelbine, or gemcitabine) until disease progression or unacceptable toxicity. Brain MRIs were required in pts with known brain metastases who were eligible if they had stable CNS disease for ≥4 wk by MRI. Per protocol, stable disease was defined as ≥2 wk from discontinuation of antiseizure medication and corticosteroid dose (≤20 mg prednisone equivalent) that was stable or decreasing for ≥2 wk before randomization. In these pts, brain MRIs were required throughout the study. The primary endpoint was progression-free survival (PFS) per independent central review (RECIST v1.1) in brain metastases-negative pts. Secondary endpoints included PFS per investigator assessment, PFS in the full population (in pts with/without brain metastases) by central review, objective response rate (ORR), overall survival (OS), and safety. Results: Overall, 61 of 529 (12%) enrolled pts had stable brain metastases at screening and were randomized to SG (n=32) or TPC (n=29). Median age was 53 y for SG and 51 y for TPC; all pts were female and had a median of 5 prior anticancer regimens. In this subset, median PFS was 2.8 mo (95% CI, 1.5-3.9) for SG vs 1.6 mo (95% CI, 1.3-2.9) for TPC by central review, and median OS was 6.8 mo (95% CI, 4.7-14.1) for SG vs 7.5 mo (95% CI, 4.7-11.1) for TPC. ORR for SG vs TPC, respectively, was 3% (1/32) vs 0% by central review, with a clinical benefit rate of 9.4% vs. 3.4%. Stable disease was achieved in 15 (47%) pts with SG vs 9 (31%) pts with TPC. In 53 pts who received at least 1 dose of treatment (SG, n=30; TPC, n=23), any-grade treatment-emergent adverse events (>20% with SG) for SG vs TPC were fatigue (63% vs 52%), diarrhea (50% vs 13%), neutropenia (43% vs 35%), nausea (43% vs 26%), decreased appetite (30% vs 17%), decreased neutrophil count (33% vs 22%), anemia (23% vs 35%), alopecia (23% vs 13%), and constipation (23% vs 22%). There were no treatment-related deaths. Two pts treated with SG are continuing study treatment for 16.2 and 6.3 mo as of the data cutoff date. Conclusions: Data interpretation in this population with poor prognosis is limited by the small sample size. In this exploratory analysis of pts with brain metastases from the phase 3 ASCENT study, SG was numerically better than TPC for tumor response and PFS but not OS. The safety profile was similar to that of the population without brain metastases for both study arms. SG is currently under clinical investigation for pts undergoing elective craniotomy for breast cancer with brain metastases or recurrent glioblastoma (NCT03995706) based on promising preclinical and intracranial clinical data. Citation Format: Véronique Diéras, Robert Weaver, Sara M. Tolaney, Aditya Bardia, Kevin Punie, Adam Brufsky, Hope S. Rugo, Kevin Kalinsky, Tiffany Traina, Leonard Klein, Delphine Loirat, Filipa Lynce, Brooke Daniel, Foluso Ademuyiwa, Sara A. Hurvitz, David M. Goldenberg, Quan Hong, Martin Olivo, Loretta M. Itri, Lisa Carey. Subgroup analysis of patients with brain metastases from the phase 3 ASCENT study of sacituzumab govitecan versus chemotherapy in metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD13-07.

Clinical Trials.gov Identifier, NCT00789581.

Ramucirumab combined with eribulin did not significantly improve PFS in advanced MBC.

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TPS1106 Background: Immune checkpoint inhibitors (ICIs) have not yet benefited most patients with breast cancer. In mTNBC, ICIs combined with chemotherapy have improved survival only in PD-L1+ mTNBC. The optimal ICI combination agent to overcome primary resistance in PD-L1– mTNBC is unknown. One promising agent is the anti-Trop-2-SN-38 antibody drug conjugate (ADC) SG, which led to median progression-free survival (PFS) of 5.6 months in mTNBC with ≥2 prior lines of chemotherapy.1 This ADC may boost anticancer immunity by binding immune cell receptors to promote antibody-dependent cellular cytotoxicity.2 In addition, the SN-38 payload of SG is the active metabolite of irinotecan, which depletes regulatory T cells, upregulates MHC class I and PD-L1 expression, and augments the antitumor activity of anti-PD-1/L1 antibodies in murine tumor models.3 The irinotecan analogue camptothecin also enhances CD8+ cytotoxic T cell effector functions and antitumor immune responses by inhibiting NR4A transcription factors,4 which have recently been shown to play a central role in inducing the T cell dysfunction associated with chronic antigen stimulation in solid tumors. Methods: This is a multi-center 1:1 randomized phase II trial to investigate whether the addition of pembrolizumab (200 mg IV every 3 weeks) to SG (10 mg/kg IV days 1+8 every 21 days) improves PFS compared to SG alone in mTNBC that is PD-L1– by standard of care testing with 22C3 CPS < 10 or SP142 immune cells < 1% (NCT04468061). Key eligibility criteria include no prior systemic therapy for mTNBC and evaluable disease. Previously treated brain metastases are permitted. Exclusion criteria include prior treatment with SG, irinotecan, and PD-1/L1 inhibitors. Based on a sample size of 110 patients per arm, the trial has 80% power to detect a 3-month difference in median PFS from 5.5 months in the SG-alone cohort to 8.5 months in the SG + pembrolizumab cohort with a one-sided alpha of 0.1. Participants undergo mandatory baseline and on-treatment research biopsies if their disease is safely accessible. Tumor biopsies will be evaluated for Trop-2, immune cells, inhibitory checkpoints, transcriptomic signatures, and genomic alterations. Stool specimens will be submitted for microbiome analyses, and health-related quality of life will be assessed. The trial is currently open and enrolling patients. References: 1) Bardia A et al. Ann Oncol 31, S1142-S1215 (2020). 2) Cardillo TM et al. Bioconjug Chem 26, 919-931 (2015). 3) Iwai T et al. Oncotarget 9, 31411-31421 (2018). 4) Hibino S et al. Cancer Res 78, 3027-3040 (2018). Clinical trial information: NCT04468061 .

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