Open AccessSYST-06. PHASE II TRIAL OF PAXALISIB (GDC-0084) IN COMBINATION WITH TRASTUZUMAB FOR PATIENTS WITH HER2-POSITIVE BREAST CANCER BRAIN METASTASES (BCBM)
Author(s) -
José Pablo Leone,
Nabihah Tayob,
Alyssa Pereslete,
Jennifer A. Ligibel,
Heather A. Parsons,
Wenya Linda Bi,
Jean J. Zhao,
Eric P. Winer,
Nancy U. Lin
Publication year - 2021
Publication title -
neuro-oncology advances
Language(s) - English
Resource type - Journals
ISSN - 2632-2498
DOI - 10.1093/noajnl/vdab112.034
Subject(s) - trastuzumab , medicine , cohort , clinical endpoint , brain metastasis , oncology , breast cancer , metastatic breast cancer , pten , cancer , metastasis , pi3k/akt/mtor pathway , clinical trial , biology , apoptosis , biochemistry
BACKGROUND The PI3K/Akt/mTOR is an important pathway in BCBM. Mutations in PIK3CA or PTEN loss are associated with trastuzumab resistance. Inhibition of PI3K and mTOR led to durable responses in 3 of 5 patient-derived xenografts (PDX) models of BCBM. Paxalisib is a potent, brain-penetrant inhibitor of class I PI3K and mTOR. METHODS This is a single-center, phase II study to evaluate the efficacy of the combination of paxalisib with trastuzumab for the treatment of central nervous system (CNS) metastases in patients with HER2-positive breast cancer. Patients will receive paxalisib (45 mg daily) and trastuzumab (8 mg/kg loading dose, then 6 mg/kg every 3 weeks). Two cohorts will be enrolled: Cohort A: a single-arm, two-stage, phase II cohort; and Cohort B: a pre-surgical window cohort. Inclusion criteria include unequivocal evidence of new and/or progressive HER2-positive CNS metastases, at least one measurable (≥10 mm) CNS metastasis (Cohort A), clinical indication for CNS metastasis resection (Cohort B). Primary endpoint for Cohort A is objective response rate (ORR) in the CNS per Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) criteria. For Cohort B, the primary endpoint is the correlation between p4EBP1 levels in the resected CNS tumor tissue from patients and intracranial response to paxalisib/trastuzumab in the PDX model generated from the same patient. Secondary endpoints include overall survival, safety and patient-reported outcomes. Mandatory blood and cerebrospinal fluid with optional tumor biopsy will be collected at baseline, on-treatment and at progression. In Cohort A, we will enroll 37 patients in a Simon two-stage design. If ≥4 responses are seen, the regimen will be considered successful. This design has 90% power with alpha <10%. Cohort B will enroll 10 patients. The trial opened in February, 2019 and 8 patients have been enrolled. NCT03765983.