Abstract PS08-01: Antibody-Drug Conjugates (ADCs) in Breast Cancer: Real World Analysis of Outcomes

Abstract Methods: We estimated the distribution of progression-free survival (PFS), overall survival (OS), and time to treatment failure (TTF) using the Kaplan-Meier method. Differences in survival curves between groups categorized by initial ADC treatment and subsequent ADC treatments were assessed using the log-rank test. Cox proportional hazards regression models were employed to evaluate the association between each survival outcome and various measures of interest, such as age, gender, race, number of prior lines of treatment, hormone receptor status, and HER2 status. Results: The analysis included a total of 469 breast cancer patients, with the distribution of clinical characteristics summarized in Table 1. The median age at the start of ADC treatment was 50 years (range: 20-85). Among the patients, 263 patients (56%) received SC as their initial ADC treatment, while 44% received T-DXd. Additionally, 29 patients received both ADCs during metastatic treatment. The median follow-up time for all patients was 7.9 months (range: 0.1- 39.1). Out of the total patient population, 29% died, while 71% were still alive at the last follow-up. The median OS for all patients was 21.6 months. Median OS of patients receiving SC or T-DXd as their initial ADC treatment, was 14 and 37.1 months, respectively. Patients who received both SC and T-DXd had a median OS of 26.1 months. The median PFS for all patients was 6.0 months. Patients initially treated with SC had a median PFS of 4.7 months, whereas those treated with T-DXd had a median PFS of 9.0 months. In patients who received both, median of PFS was 4.9 months for T-DXd after SC, and 5.0 months for SC after T-DXd. The median TTF for all patients was 6.1 months. Patients initially treated with SC had a median TTF of 4.7 months, while those treated with T-DXd had a median TTF of 9.0 months. In patients who received T-DXd after SC, TTF was 4.9 months and SC after T-DXd was 5.0 months. Clinician-judged responses were seen in 180 (74%)of patients with SC only, 80 (41%) with T-DXd only, 9 (100%) with SC as 2nd ADC and 20 (100%) with T-DXd as 2nd ADC. Furthermore, the analysis explored the association of OS, PFS, and TTF with various measures of interest, including age, gender, race, number of prior lines of treatment, type of treatment, hormone receptor status, HER2 status, Ki67, and best response to ADC. Some notable associations were observed, such as ER-positive status being associated with marginally longer OS compared to ER-negative status (median 24.7 vs. 16.4 months; p=0.06), and HER2-positive status being associated with longer PFS compared to HER2-negative status (median 14.2 vs. 5.4 months; p 0.001). However, these associations should be interpreted cautiously as they were obtained from univariate analysis. Conclusions: Overall, these results highlight the significant differences in survival outcomes between different ADC treatments in breast cancer patients, likely due to differing patient characteristics. Distribution of clinical characteristics across ADCs Citation Format: Akshara Singareeka Raghavendra, Zhongya Wang, Roland Bassett, Debu Tripathy. Antibody-Drug Conjugates (ADCs) in Breast Cancer: Real World Analysis of Outcomes 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 PS08-01.