TRIO-US B-12 TALENT: Phase II neoadjuvant trial evaluating trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early-stage breast cancer.

TPS623 Background: Although patients with hormone receptor-positive (HR+)/HER2-negative breast cancer (BC) frequently experience disease response to neoadjuvant therapy, fewer than 10% achieve a pathologic complete response (pCR) with standard chemotherapy or endocrine therapy, even in combination with CDK4/6 inhibitors. Thus, finding more effective therapies for this disease remains an area of unmet need. HER2 amplification is a known driver of endocrine resistance and HER2 may be expressed at a low level (IHC 1+ or 2+) in approximately 60% of HR+ BC. Trastuzumab deruxtecan (DS-8201a, T-DXd) is a novel HER2-targeting antibody drug conjugate (ADC) that is FDA approved in the US for HER2-positive (with boxed warnings for interstitial lung disease) and has demonstrated promising clinical efficacy in HER2-low BC with an objective response rate of ̃37%. The aim of TALENT (TRIO-US B-12, NCT04553770) is to evaluate the clinical activity and safety of neoadjuvant T-DXd alone or in combination with endocrine therapy in patients with HR+/HER2-low early BC. Methods: This is an ongoing randomized, multicenter, open-label, two-stage, phase II neoadjuvant trial for participants with early stage, HR+, HER2-low (1+ or 2+/ISH- by IHC) BC. Eligible participants include men and women with previously untreated, operable invasive BC greater than 2.0 cm (cT2). Pts with recurrent, metastatic, or inflammatory BC are excluded. Pts are randomized 1:1 to receive six to eight cycles of T-DXd (5.4 mg/kg IV q21 days) alone or in combination with anastrozole AI (1 mg PO QD). Men and pre/peri menopausal women randomized to the AI arm also receive routine care GnRH agonist. Stratification factors include HER2 expression and menopausal status (men stratified as postmenopausal). Tumor tissue is taken at baseline, cycle 1 day 17-21, and at surgery. Blood samples are taken at 4 time points for biomarker analysis. The primary endpoint is pCR rate (breast and lymph node) at definitive surgery. In stage I, 58 participants will be randomized (29/arm). If >2 participants in an arm achieve pCR, that arm will expand (stage II) to enroll an additional 15 participants (total of 44/arm). A pCR rate of > 10% (5/44) would be considered favorable, warranting further evaluation in a larger trial. Other endpoints include safety, changes in Ki67 expression, Residual Cancer Burden index, biomarker analysis (including serial cfDNA analysis), and health-related quality of life. As of January 2022, 37 participants have enrolled, 24 have completed treatment, and 14 have had surgery. To our knowledge this is the first and only ongoing study evaluating T-DXd with or without endocrine therapy for HR+, HER2-low BC in the neoadjuvant setting. The study will shed light on clinical activity and biomarkers, which may guide larger confirmatory studies for this population. Clinical trial information: NCT04553770.