Exploratory subset analysis according to prior endocrine treatment of two randomized phase II trials comparing gefitinib (G) with placebo (P) in combination with tamoxifen (T) or anastrozole (A) in hormone receptor-positive (HR+) metastatic breast cancer (MBC)

1014 Background: Preclinical and clinical data suggest that increased EGFR and HER-2 activity contribute to acquired resistance to endocrine therapy. Strata of two clinical trials recently showed that the addition of G to T or A in HR+ MBC prolonged progression free-survival (PFS). Certain preclinical data also suggested that G should be combined with T or A from the start of endocrine therapy rather than waiting for resistance to develop. To examine this clinically a post hoc analysis compared the subsets of patients (pts) who had received prior endocrine therapy (may have already upregulated HER receptors) to those that were endocrine therapy naive (not yet upregulated HER receptors). Methods: One trial evaluated G (250 mg/day orally) + A (1 mg/day orally) versus A+P (NCT00077025) and one trial evaluated G (250 mg/day orally) + T (20 mg/day orally) versus T+P (NCT00229697). Post hoc analysis of PFS was performed in two pt subgroups; previously treated with endocrine therapy (ET) and endocrine naive (EN)...