Abstract PO4-18-04: An exploratory study of Trastuzumab Deruxtecan neoadjuvant therapy in HER2-positive or HER2-low early or locally advanced breast cancer after a poor response to neoadjuvant chemotherapy

Abstract Background The current standard of care for neoadjuvant treatment of HER2-positive early-stage breast cancer consists of dual HER2-blockade with trastuzumab (H) plus pertuzumab (P) and polychemotherapy with a pathological complete response (pCR) rate of 31%~50%. Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate composed of an anti-HER2 antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor. T-DXd significantly prolonged progression-free and overall survival vs trastuzumab emtansine in HER2-positive unresectable and/or metastatic breast cancer (mBC) previously treated with H and taxane in DESTINY-Breast03 study. HER2-low breast cancer is currently treated as HER2-negative (HER2-low and HER2-zero) breast cancer, with patients stratified according to hormone-receptor (HR) status. In DESTINY-Breast04 study, T-DXd resulted in significantly longer progression-free and overall survival than the physician’s choice of chemotherapy in HER2-low mBC. Given the efficacy of T-DXd monotherapy in HER2-positive or HER2-low mBC, we conduct an exploratory study to evaluate the efficacy and safety of T-DXd in HER2-positive or HER2-low early or locally advanced breast cancer after a poor response to neoadjuvant chemotherapy, and to identify sensitive biomarkers for T-DXd neoadjuvant therapy. Methods Eligible patients were women aged 18 years to 75 years with clinical stage cT2–cT4/cN0–cN3/cM0 (stage II–III) invasive breast cancer (2 cm in size) confirmed as HER2-positive (immunohistochemistry IHC 3+) or HER2-low (IHC2+ or IHC1+/situ hybridization-negative). Patients are required to have an Eastern Cooperative Oncology Group performance status of 0 or 1, and baseline left ventricular ejection fraction of at least 55% (as measured by echocardiogram). Patients are also required to have adequate organ function and bone marrow function. Patients with HER2-positive breast cancer should receive taxane (paclitaxel or nab-paclitaxel) or docetaxel, carboplatin, and H plus P for 2 cycles. Patients with HER2-low and HR-positive breast cancer should receive taxane (paclitaxel or nab-paclitaxel) or docetaxel, and cisplatin or carboplatin for 2 cycles. Patients with HER2-low and HR-negative breast cancer should receive taxane (paclitaxel or nab-paclitaxel) or docetaxel, and anthracycline (epirubicin, pirarubicin or liposomal doxorubicin) for 2 cycles. For patients who have responses of stable disease assessed by magnetic resonance imaging will receive T-DXd neoadjuvant therapy. T-DXd will be administered intravenously every 3 weeks at a dose of 5.4 mg per kilogram of body weight for 4 cycles. Peripheral blood and biopsy tissue will be collected before neoadjuvant chemotherapy and T-DXd neoadjuvant therapy, and peripheral blood and surgical tissue will be collected after the surgery. Lipid metabolites in peripheral blood and mass spectrometry-based protein quantification in tissue will be detected to find sensitive biomarkers for T-DXd neoadjuvant therapy. The primary endpoint is pCR rate (ypT0/Tis ypN0) and identify sensitive biomarkers for T-DXd neoadjuvant therapy. Secondary endpoints include objective response rate, breast-conserving rate and invasive disease-free survival. Citation Format: Jin Zhang, Zhendong Shi, Jingjing Liu. An exploratory study of Trastuzumab Deruxtecan neoadjuvant therapy in HER2-positive or HER2-low early or locally advanced breast cancer after a poor response to neoadjuvant chemotherapy abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-18-04.