Abstract PO3-17-07: Real-world experience with trastuzumab deruxtecan in patients with breast cancer: 6 month-interim analysis of an all-patient postmarketing surveillance in Japan

Abstract Background: Trastuzumab deruxtecan (T-DXd) is an anti-human epidermal growth factor receptor 2 (HER2) antibody-drug conjugate. T-DXd has shown great efficacy in HER2-positive breast cancer, hence receiving approval in Japan in March 2020. In Japan, all-patient postmarketing surveillance (PMS) is underway to evaluate the risk of interstitial lung disease/pneumonitis (ILD/p) in patients with breast cancer treated with T-DXd. Due to the limited generalizability of results from clinical trials, there is a need for more information about ILD/p in a real-world setting. Herein we present an interim analysis of the large-scale all-patient PMS. Methods: This is an observational, multicenter, all-patient PMS (jRCT1080225197) with an observation period of 18 months that enrolled all patients treated with T-DXd for recurrent/advanced HER2-positive breast cancer. Patients who initiated T-DXd treatment between May 2020 (launch date of T-DXd) and May 2021 were included in the interim analysis to ensure the observation period of 6 months from the initial treatment of T-DXd. This interim analysis is based on safety data from the first 6 months of 1204 patients. Data collected includes baseline characteristics and information on ILD/p. All potential ILD/p (identified based on the AE terms) reported by physicians were adjudicated by an independent ILD adjudication committee. The incidence of ILD/p was calculated from adjudicated drug-related ILD/p. Results: The interim analysis set included 1204 patients with median age of 60 years. Three of the 1204 patients (0.2%) received T-DXd as a first-line treatment, 30 (2.5%) as second-line, 1159 (96.3%) as third- line or later treatment. At baseline, 105 (8.7%) of patients had an Eastern Cooperative Oncology Group performance status (ECOG PS) 2 or greater, 8 (0.7%) had severe renal impairment (15≤ creatinine clearance (CLcr) < 30 mL/min), 4 (0.3%) had end-stage renal disease (CLcr < 15 mL/min), 5 (0.4%) had severe liver impairment (total bilirubin >4.5 mg/dL), and 32 (2.7%) had comorbid ILD/radiation pneumonitis. Those were defined as exclusion criteria in clinical trials of T-DXd. The median dose at the start of administration of T-DXd was 5.4 mg/kg (range:2.7-5.4). During the first 6 months from the initial treatment, T-DXd was discontinued in 403 (33.5%) of the 1204 patients. The most common reasons for discontinuation were disease progression in 232 (57.6%) of the discontinued 403 patients followed by ILD/p in 97 (24.1%) of the 403 patients. In the first 6 months, the incidence of all grade, grade ≥3, and grade 5 ILD/p were 8.2% (n=99), 1.7% (n=20) and 0.4% (n=5), respectively. The incidence of ILD/p stratified by baseline characteristics identified as potential risk factors of drug-related ILD/p is shown in Table. Conclusion: This is the first report demonstrating real-world experience with T-DXd in Japan. The interim analysis revealed useful information including patient and treatment profiles of T-DXd and the incidence of ILD/p during the first 6 months from the initial treatment in a real-world setting in Japan. The final analysis of the ongoing PMS is warranted for further evaluation. Incidence of interstitial lung disease/pneumonitis by patient baseline characteristics XX XX ILD/p: interstitial lung disease/pneumonitis, 95% CI: 95% confidence interval, CLCr: creatinine clearance using the Cockcroft-Gault equation * includes ILD/p, pulmonary fibrosis, radiation pneumonitis, chronic obstructive pulmonary disease, emphysema, and Asthma (Source: Powell CA, Modi S, Iwata H, et al. Pooled analysis of drug-related interstitial lung disease and/or pneumonitis in nine trastuzumab deruxtecan monotherapy studies. ESMO Open 2022;7(4):100554) Citation Format: Junji Tsurutani, Hideki Mizutani, Ayumi Tanabe. Real-world experience with trastuzumab deruxtecan in patients with breast cancer: 6 month-interim analysis of an all-patient postmarketing surveillance in Japan [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 PO3-17-07.