Pazopanib (PZ) plus endocrine therapy as treatment for hormone resistant advanced breast cancer (ABC).

Abstract

1068 Background: A major limitation of endocrine therapy in hormone receptor positive (HR+) ABC is the development of resistance. 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) of PZ, a VEGF receptor tyrosine kinase inhibitor (TKI) combined with 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 < 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 planned 28. Results: 32 pts were enrolled; 28 are evaluable for study endpoints and all patients completed the study. The median age was 58 years (range: 41-77). Pts were heavily pre-treated, with a median of 2 prior hormone therapies (range 1-6) and 1 prior chemotherapy (range 0-8). 8 pts (28.6%) stopped treatment due to adverse events (AE) including hypertension (HTN), fever, transaminitis, nausea, vomiting, rash, hand foot syndrome and pulmonary embolism (PE); 6 pts progressed before wk 12. CBR12 was 46.4% (12 SD, 1 PR); CBR24 was 25% (5 SD, 2 PR). Median PFS was 20 wks (95% CI 11-48, and median PFS for pts with CBR12 was 24 wks. 7 pts had PFS > 6 months (24, 32, 36, 36, 48, 184 and 274 wks); 2 pts had PFS > 3 years (184 and 274 weeks). The most common grade 1/2 AE were nausea (48.2%), fatigue (33.3%), diarrhea (29.6%), back pain (22.2%), and arthralgias (22.2%). Grade 3/4 AEs included HTN (3/28; 11.1), transaminitis (3/28; 11.1%), headache (2/28; 7.4), heart failure, vertigo, nausea, oral pain, vomiting, fever, fatigue, and hypokalemia (one patient each: 3.7%). Conclusions: The addition of PZ to NSAIs resulted in a CBR12 of 46.4%, and a CBR24 of 25% in pts with heavily pre-treated ABC resistant to NSAIs. These results support clinical efficacy of antiangiogenic TKI in HR+ ABC, and suggest benefit in hormone resistant disease. Expected toxicities resulted in early discontinuation in 28.6%, which limited drug exposure. Clinical trial information: NCT 01466972 .