Phase II randomized study of the EGFR, HER2, HER3 signaling inhibitor AZD8931 in combination with anastrozole (A) in women with endocrine therapy (ET) naive advanced breast cancer (MINT).

531 Background: Preclinical data suggest a key role for EGFR inhibition in delaying acquired resistance to ET in ER+ breast cancer (BC). Retrospective analyses of 2 Phase II studies suggested adding gefitinib to ET delayed PFS in ET naive (ETN) BC. This randomized, double-blind, placebo-controlled multi-center study (NCT01151215) was conducted to prospectively test the hypothesis that adding AZD8931, an inhibitor of EGFR, HER2 and HER3 signaling, to A would be beneficial in delaying endocrine resistance in an advanced ETN BC population. Methods: Post-menopausal women with ER+ and/or PR+, ETN, HER2-negative, advanced BC were randomized (1:1:1) to receive A (1 mg od) plus AZD8931 20 or 40 mg bd or placebo (P). The primary endpoint was PFS (ITT population). Data presented are from an interim analysis (data cutoff 31 Aug 2012; 39% pts had a progression event). Results: Between Jun 2010 and Jun 2012, 359 pts (median age 61 years) were randomized to A combined with AZD8931 20 mg (n=118), 40 mg (n=120) or P (n=121). At the interim analysis, median PFS in the AZD8931 20 mg, 40 mg and P arms was 10.9, 13.8 and 14.0 months, respectively; PFS HR (95% CI) for AZD8931 20 mg:P was 1.37 (0.91–2.06, P=0.135) and for AZD8931 40 mg:P was 1.16 (0.77–1.75, P=0.485). Deaths were reported for 20 (17%), 16 (13%) and 12 pts (10%) in the AZD8931 20 mg, 40 mg and P arms, respectively. Grade ≥3 AEs were reported for 22 (19%), 44 (37%) and 18 (15%) pts in the AZD8931 20 mg, 40 mg, and P arms, respectively, the most frequent being rash (0% vs 8% vs 2%), acneiform dermatitis (0% vs 7% vs 0%) and hypertension (3% vs 3% vs 2%). Serious AEs were reported for 12%, 14% and 9% pts in the AZD8931 20 mg, 40 mg and P arms, respectively, and discontinuation (of AZD8931 or P) due to an AE in 5%, 8% and 2% pts, respectively. Conclusions: Co-blockade of EGFR, HER2, HER3 in combination with aromatase inhibition does not appear to delay endocrine resistance to ETN BC. Based on the low probability of demonstrating superior efficacy with addition of AZD8931 to A and the overall risk/benefit, the study was closed at the recommendation of the IDMC and pts discontinued AZD8931. Clinical trial information: NCT01151215.