Prospective Registry of ADC as First- and Second-line Treatment for Breast Cancer

PRIMARY OBJECTIVES: I. Real-world progression free survival (rwPFS) of the first line of ADC under routine care (ADC1) by investigator assessment II. Real-world progression free survival (rwPFS) of the second line ADC under routine care (ADC2) by investigator assessment SECONDARY OBJECTIVES: I. To evaluate the efficacy of ADC1 and ADC2 as measured by duration of response (DOR), best overall response (BOR), disease control rate (DCR), and overall survival (OS) for each ADC. II. To evaluate key safety parameters for ADC1 and ADC2 by chart review. EXPLORATORY OBJECTIVES: I. To evaluate/identify correlative biomarkers (e.g., circulating tumor DNA (ctDNA), circulating tumor cells (CTC), and tissue spatial correlates) of response/resistance to ADCs. II. To evaluate patient reported outcomes (PROs) for each ADC. OUTLINE: Participants will have medical chart reviews and biospecimens collected for the duration of routine care with ADC1 and/or ADC2. After the last dose of ADC2, participants will continue to be followed for survival data collection via chart review every 12 weeks for up to 2 years.