Addition Of Pazopanib (Pz) To Endocrine Therapy In Hormone Resistant Advanced Breast Cancer (Abc).

560Background: A major limitation of endocrine therapy is development of resistance in hormone receptor positive (HR+) ABC. Preclinical data suggests that higher levels of vascular endothelial growth factor (VEGF) are associated with endocrine therapy resistance. We conducted a phase II trial to evaluate the clinical benefit (CB) from adding PZ, a VEGF receptor tyrosine kinase inhibitor (TKI) to nonsteroidal aromatase inhibitors (NSAIs) in pts with ABC resistant to NSAIs. Methods: Eligibility included postmenopausal women with HR+ ABC and progressive disease (PD) after at least one month of NSAIs. Treatment was PZ 800 mg/day plus either letrozole or anastrozole. The primary endpoint was clinical benefit rate at 12 weeks (CBR12, wks). Secondary endpoints were PFS and safety. A CBR of 20% was considered a clinically meaningful comparison to the expected CBR of u003c 5% with continued NSAIs after PD. Using a 2-stage design, stable disease in at least 1 of the first 13 pts allowed continued enrollment to a planne...