Progression-free survival (PFS) of patients with HER2-negative, estrogen-receptor (ER)-low metastatic breast cancer (MBC) with the addition of lapatinib to letrozole: Biomarker results of EGF30008

Abstract

1018 Background: Lapatinib (Lap), an oral, dual inhibitor of EGFR/HER-2, is approved with capecitabine for treatment of HER-2+ MBC for recurrence after taxane, anthracycline, and trastuzumab-based therapy. Letrozole (Let) has activity in hormone-receptor positive (HR+) BC. It has been hypothesized that peptide growth factor signaling and hormone signaling pathways interact and dual targeting of these pathways results in therapeutic synergy. We report a blinded analysis of HER-2, ER, and progesterone receptor (PR) expression for patients (pts) with HR+ MBC at first diagnosis or post-adjuvant relapse and response to Lap + Let versus Let. Methods: 1286 pts were randomized 1:1 to 2.5 mg Let daily plus either 1500 mg Lap daily or placebo. The primary endpoint was PFS in HR+, HER-2+ MBC pts; secondary endpoints included PFS in the intent-to-treat population. Blinded, centralized commerical laboratory analysis of archived tumor tissue for HER-2 (IHC and/or FISH) and academic laboratory semi-quantitative analysis of ER/PR (IHC, H-score) was performed and correlated with clinical outcome. Results: In 219/1286 (17%) HER-2+ (FISH+ or IHC3+) pts, a significant improvement in median PFS was observed for Lap + Let versus Let (8.2 v 3.0 mos, HR = 0.71, 95% CI 0.53, 0.96, p = 0.019). No significant difference in median PFS was seen in 952 (74%) HER-2-negative pts (13.4 v 13.7 mos, HR = 0.90, 95% CI 0.77, 1.05, p = 0.188). 821/952 (86%) HER-2-negative pts had tissue available for quantitative ER and PR analysis. Analysis of ER and PR by quartile identified a subgroup of HER-2-negative pts that benefitted from adding Lap to Let. Pts with the lowest quartile of ER expression (H-score <160, n = 207) had a significant improvement in median PFS (13.6 mos v 6.6 mos, HR = 0.65, 95% CI 0.47, 0.9, p < 0.005). Pts with higher levels of ER did not significantly benefit from adding Lap to Let. Analysis of PR expression did not identfiy a subgroup that benefited from Lap. Conclusions: Pts with HER-2-negative, ER+ MBC and low ER expression may benefit from the addition of lap to let. Additional analyses of EGFR, other biomarkers, and prior hormone therapy will be presented. [Table: see text]