Wardley, AndrewCortes, JavierProvencher, LouiseMiller, KathyChien, A. JoRugo, Hope S.Steinberg, JoyceSugg, JenniferTudor, Iulia C.Huizing, ManonYoung, RobynAbramson, VandanaBose, RonHart, LowellChan, StephenCameron, DavidWright, Gail S.Graas, Marie‑PascaleNeven, PatrickRocca, AndreaRusso, StefaniaKrop, Ian E.2024-03-192024-03-192021Wardley A, Cortes J, Provencher L, et al. The efficacy and safety of enzalutamide with trastuzumab in patients with HER2+ and androgen receptor-positive metastatic or locally advanced breast cancer. Breast Cancer Res Treat. 2021;187(1):155-165. doi:10.1007/s10549-021-06109-7https://hdl.handle.net/1805/39336Purpose: Androgen receptor (AR) expression occurs in up to 86% of human epidermal growth factor receptor 2-positive (HER2+) breast cancers. In vitro, AR inhibitors enhance antitumor activity of trastuzumab, an anti-HER2 antibody, in trastuzumab-resistant HER2+ cell lines. This open-label, single-arm, phase II study evaluated the efficacy and safety of enzalutamide, an AR-signaling inhibitor, in patients with advanced HER2+ AR+ breast cancer previously treated with trastuzumab. Methods: Eligible patients had measurable or non-measurable evaluable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1, Eastern Cooperative Oncology Group status ≤ 1, no history of brain metastases, and previously received ≥ 1 anti-HER2 regimen for advanced disease. Patients received 160 mg oral enzalutamide daily and 6 mg/kg intravenous trastuzumab every 21 days until disease progression or unacceptable toxicity. Primary end point was clinical benefit rate at 24 weeks (CBR24); secondary end points included progression-free survival (PFS) and safety. Results: Overall, 103 women were enrolled [median age 60 years (range 34-83)]; 62% had received ≥ 3 lines of prior anti-HER2 therapy. CBR24, comprising patients with confirmed partial responses (5%) and durable stable disease at 24 weeks (19%), was 24% in the efficacy evaluable set (n = 89). CBR24 did not seem related to AR-expression levels or hormone receptor status. Median PFS was 3.4 months (95% confidence interval 2.0-3.8). Overall, 97 (94%) patients experienced treatment-emergent adverse events (TEAEs), with fatigue most common (34%). Dyspnea (4%) and malignant neoplasm progression (3%) were the only TEAEs grade ≥ 3 reported in ≥ 3 patients. 22 patients (21%) reported serious TEAEs. Four patients (4%) experienced fatal, non-drug-related TEAEs. Conclusions: Enzalutamide plus trastuzumab was well tolerated, and a subset of patients in this heavily pretreated population had durable disease control. Determination of biomarkers is needed to identify patients most likely to benefit from this combination.en-USAttribution 4.0 InternationalAndrogen receptorEnzalutamideHuman epidermal growth factor receptor 2HER2Metastatic breast cancerTrastuzumabArticle