Final results from a phase II evaluation of lapatinib (L) and bevacizumab (B) in HER2-overexpressing metastatic breast cancer (MBC).

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #3133 Background: HER2 overexpression has been shown to upregulate VEGF expression in pre-clinical breast cancer models. Overexpression of both HER2 and VEGF has been associated with worse clinical outcome than overexpression of either receptor alone. In pre-clinical models, combination anti-HER2 and anti-VEGF therapy has been shown to be more effective than either treatment alone. B plus trastuzumab (T) has shown promising activity in patients (pts) with HER2+ MBC, however the cardiac toxicity of this regimen requires further study. L, an oral dual tyrosine kinase inhibitor of EGFR and HER2, is approved in combination with capecitabine after T-based therapy for HER2+ MBC. L may have less cardiac toxicity and may be a safer and more effective alternative to T. This hypothesis was evaluated in a phase 2 trial of L+B in HER2+ MBC pts. Methods: This single-arm study was designed to evaluate L (1500 mg PO daily) plus B (10 mg/kg IV q2wk) in 50 HER2+ MBC patients. The primary endpoint is crude progression-free survival (PFS) rate at 12 weeks with 84% power to detect a clinically significant PFS rate of 60%; secondary endpoints include toxicity and response per RECIST. Efficacy was assessed at Week 6, 12, and q12wks thereafter. HER2-overexpression was defined as local FISH-positive or IHC 3+ results. Serial evaluation of circulating tumor and endothelial cells and HER2 extracellular domain was performed. Results: Enrollment to this study ended in March 2008 (n=52). Data are presently available on 32 of 52 pts enrolled before January 1, 2008. Pts received a median of 5 prior MBC therapies (range 0-15); 88% received prior T (median 19.7 months; range 1.2-56.8 months). The most frequently reported AEs included diarrhea (81%), rash (66%), nausea (56%), fatigue (56%), and emesis (46%). Four asymptomatic LVEF declines were reported (three grade 2 events; one grade 1 event), as were nine cases of hypertension (eight grade 1 or 2 events; one grade 3 event) and one grade 3 GI hemorrhage. 27/32 patients were evaluable for response; five withdrew prior to first radiologic assessment (two due to toxicity, three due to investigator/pt request). The crude 12-week PFS rate was 63% (20/32 did not progress by Week 12); overall response rate (complete/partial response) was 13%, and the clinical benefit rate (complete/partial response or stable disease for ≥ 24 weeks) was 34%. Conclusions: L+ B is well tolerated and has shown promising activity in heavily pretreated HER2+ MBC pts. Final efficacy and safety data will be presented on the full study cohort. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3133.