Abstract PO4-05-10: A Carryover Effect: Antibody Drug Conjugates Constantly Provide a Substantial Improvement in Overall Survival more than in Progression-free Survival

Abstract Background: In metastatic breast cancer (MBC), progression-free survival (PFS) improvement does not always translate into overall survival (OS) benefit. Multiple treatment options after progression resulted in a long post-progression survival in MBC patients, and these would make the dissociation of PFS benefit and OS benefit. We have reported the constant correlation of PFS improvement and OS improvement in anti-HER2 containing treatment (Breast 2021; 59:211-220). The relationship between PFS and OS improvement in antibody drug conjugate has not been thoroughly examined. Methods: “Metastatic breast cancer” and “antibody drug conjugate” (ADC) were used as keywords to search for randomized clinical trials that report both PFS and OS. Hazard ratios (HR) and median survival were analyzed. Increments in PFS (delta PFS) and increments in OS (delta OS) were compared between studies. Results: A total of 8 trials were identified and summarized in table 1. The target of ADC was HER2 (N=6) or Trop2 (N=2). In DESTINY-Breast 03 trial, the control arm was another ADC (T-DM1). The control arms in all the other 7 trials were chemotherapy. The HR of PFS (range 0.28-0.66) was smaller than HR of OS (range 0.48- 0.83) in all of the trials. The median OS was not reached (NR) in 1 of the trials (DB-03) and was thus removed from the analysis for delta PFS and delta OS. In the comparison of delta PFS, the increments of median PFS fell between 1.5 and 10.9 months(m). The increments of median OS were between 1.6 and 12.7 m. All the delta OS are greater than the delta PFS in the 7 trials with available PFS and OS data. Conclusion: In MBC, ADCs targeting HER2 and Trop2 both constantly provide improvement of OS greater than PFS. Further investigation on the potential mechanism is warranted. Table 1 Citation Format: I-Chun Chen, Ching-Hung Lin, Yen-Shen Lu. A Carryover Effect: Antibody Drug Conjugates Constantly Provide a Substantial Improvement in Overall Survival more than in Progression-free Survival 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 PO4-05-10.