Studies about DS-8201 have shown that patients who had advanced human epidermal growth factor receptor 2 (HER2)-low breast cancer refractory to standard therapies can achieve clinically significant benefits by novel HER2 antibody-drug conjugate (ADC). This conclusion not only further refines the classification of breast cancer, but also triggers the consideration of redefining the criteria for HER2 expression status. At the same time, in-depth research and development of novel ADCs is becoming a new hot issue and has received much clinical attention. In this paper, on the basis of reviewing the research history of HER2-low breast cancer and the current status of ADCs research and development, combined with our research data, we explore the clinicopathological features, diagnosis and treatment progress of HER2-low breast cancer.