This is a multicenter, retrospective real-world study aiming to evaluate the efficacy and safety of post-antibody-drug conjugate (post-ADC) treatment strategies in patients with HER2-low advanced breast cancer who have developed resistance to prior ADC therapy. The study plans to enroll approximately 220 eligible patients from three centers in China (Jiangsu Province Hospital, Nanjing Drum Tower Hospital, and Nanjing General Hospital of Nanjing Military Command) between January 2018 and December 2025. Key efficacy outcomes include progression-free survival (PFS), overall survival (OS), objective response rate (ORR), and clinical benefit rate (CBR). Safety outcomes include the incidence of grade 3/4 adverse events and serious adverse events. Subgroup analyses will compare different post-ADC regimens (e.g., alternative ADC, chemotherapy, endocrine therapy, immunotherapy) and explore the impact of visceral metastasis and prior ADC treatment response on subsequent outcomes. This study seeks to identify optimal post-ADC treatment strategies and preferred patient populations for clinical benefit.