Abstract OT2-07-04: A phase 1b study of poziotinib in combination with T-DM1 in women with advanced or metastatic HER2-positive breast cancer
Authors: Bhat G , Potter D , Bharadwaj J , Khan N , Shabazz L , Tache J , Yang Z 
Published: May 2019

Background:Poziotinib represents a new class of irreversible quinazoline inhibitors of ErbB receptor tyrosine kinases that inhibit the proliferation of tumor cells in culture and in vivo by inhibiting HER-1 (EGFR), HER-2, HER-4. ErbB signaling plays important roles in the progression of HER2+ breast cancer. Poziotinib has promising clinical activity in breast cancer, and other solid tumors including lung, gastric, and colorectal cancers.

Study SPI-POZ-101, is being conducted to evaluate the safety and efficacy of the combination of daily poziotinib and T-DM1, HER2 antibody-drug-conjugate every three weeks in patients with HER2+ advanced or metastatic breast cancer.

Trial Objectives and Design: The primary objectives of the study are to determine the maximum tolerated dose (MTD) or maximum administered dose (MAD) of daily poziotinib plus T-DM1 (every 3 weeks) in women with advanced or metastatic HER2 positive breast cancer; and to evaluate the Objective Response Rate (ORR) in these patients.

The secondary objectives include disease control rate (DCR), progression-free-survival (PFS), safety and pharmacokinetics at the MTD/MAD dose level of poziotinib plus T-DM1.

In Part 1, the dose of poziotinib plus standard dose of T-DM1 (3.6 mg/kg IV) on Day 1 of each cycle will be determined using a “3+3” design with up to 3 escalating dose levels, 8, 10 and 12 mg with no DLT or to de-escalate to 6 mg with DLT observed in Cycle 1. Patients in current dose cohort, if not discontinued, will continue treatment until discontinuation of therapy.

In Part 2 of the study, approximately 10 patients will be treated at the MTD/MAD to confirm dose for safety of the combination and to evaluate preliminary efficacy.

Eligibility Criteria: The study will enroll female patients between 18 and 90 years with confirmed HER2 overexpression or gene-amplified tumor via immunohistochemistry [IHC] with IHC 3+ or IHC 2+ with confirmatory fluorescence in situ hybridization [FISH]+ or [ISH]+ and must have had at least 2 lines of anti-HER2 directed therapies either in the metastatic or early-stage disease setting. Patients must have adequate hematologic, hepatic, cardiac and renal functions and have at least one measurable lesion per RECIST 1.1 criteria. Exclusion criteria includes unstable CNS metastases or seizure disorder; anticancer chemotherapy, TKIs, biologics, immunotherapy, radiotherapy, or investigational treatment within 15 days; ≥ Grade 2 adverse events; known hypersensitivity to receptor tyrosine kinase inhibitors or any of the components of poziotinib tablets or T-DM1 IV solution.

Statistical Methods: Part 1 of the study will enroll 3 to 6 patients at each dose using 3+3 design. Part 2 will enroll 10 patients at the MTD/MAD. The efficacy analysis will be conducted using the Evaluable Population based on RECIST 1.1. The Clopper-Pearson 95% confidence interval will be estimated using exact method based on binomial distribution.

Target Accrual:Part 1: 6-18 patients Part 2: 10 patients

ClinicalTrials.gov Identifier: NCT03429101

Contact Information: Spectrum Pharmaceuticals. SPI-POZ-101@sppirx.com

Poziotinib is currently under clinical investigation and has not been approved for use in breast cancer.

Citation Format: Bhat G, Potter D, Bharadwaj J, Khan N, Shabazz L, Tache J, Yang Z. A phase 1b study of poziotinib in combination with T-DM1 in women with advanced or metastatic HER2-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT2-07-04.