Abstract P4-13-19: Poziotinib, an oral, irreversible pan-HER inhibitor, demonstrates promising clinical activity in metastatic HER2 positive breast cancer patients

Abstract

Abstract Background: Poziotinib is a novel, oral, irreversible pan-HER inhibitor that has been studied in two completed Phase 1 clinical trials in patients with advanced solid tumors (HM-PHI-101; HM-PHI-102) and is currently being studied in several Phase 2 clinical trials. Preclinical studies have shown poziotinib to be more potent in vitro than other EGFR- and HER2-directed tyrosine kinase inhibitors. This study collates the clinical experience of poziotinib in patients with advanced HER2 positive breast cancer from the two completed Phase 1 trials. Results: The maximum tolerated dose (MTD) and safety of poziotinib were evaluated in HM-PHI-101 (once daily, Day 1-14 q3 weeks) and in HM-PHI-102 (continuous dosing). The Dose Limiting Toxicity (DLT) was diarrhea in both studies. Anti-diarrheal medicine was allowed, but prophylactic anti-diarrheal therapy was not used. The most frequently reported Grade 3 AE was diarrhea (40%). The MTD for intermittent dosing of poziotinib was 24 mg and the MTD for continuous dosing was 16 mg. The Dose Limiting Toxicity (DLT) was diarrhea in both studies. Anti-diarrheal medicine was allowed, but prophylactic anti-diarrheal therapy was not used. In total, 10 patients with HER2 positive metastatic breast cancer were treated in the two trials (median age 56.5, range 30-69). These patients were heavily pretreated (median number of previous treatment regimens 5, range 3-9), and all patients had failed treatment with both trastuzumab and lapatinib. The Overall Response Rate (ORR) in these breast cancer patients was 60% and Clinical Benefit Rate (CBR) was 80%. The median duration of response was 32.5 weeks (range 18 - 56 weeks). Two patients in the early dose cohorts of 1 or 2mg had progressive disease. The median progression free survival (PFS) was 28 weeks (6, 6, 12, 17, 25, 31, 37, 49, 57, and 98 weeks). Conclusions: Poziotinib showed very promising clinical activity in Phase 1 patients with metastatic HER2 positive breast cancer, who had been heavily pretreated and failed two prior HER2-directed therapies. The ORR in this patient population was 60% and the CBR was 80% in these two early dose finding studies. The AEs observed in these studies was consistent with other pan-HER and EGFR inhibitors. While the majority of DLT cases involves diarrhea, toxicity of other adverse events was relatively tolerable. An intermittent dosing schedule seemed appropriate for poziotinib. Multiple Phase 2 studies with poziotinib are ongoing in patients with breast cancer and other solid tumors. Citation Format: Im S-A, Kim J-H, Lee K-H, Kim SH, Oh D-Y, Kim Y-J, Han S-W, Kim T-Y, Kim T-Y, Jung J, Bang Y-J. Poziotinib, an oral, irreversible pan-HER inhibitor, demonstrates promising clinical activity in metastatic HER2 positive breast cancer patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-13-19.