Correlation Study of Serum HER 2 Against HER 2-ADC Drug Efficacy in HER 2 Low-expressing Breast Cancer

ADC drugs are a new type of targeted therapy. ADC drugs are composed of monoclonal antibodies, linkers and drug carriers, which bind to the target antigen on the surface of tumor cells through antibodies, endocytosis/internalization to form early endosomes in cells, and then mature into late endosomes and fuse with lysosomes. ADC drugs break apart in the lysosome and release the drug carrier, eventually leading to apoptosis or death while minimizing damage to normal cells. However, not all subjects with HER2-positive breast cancer respond well to ADC drugs, and resistance may develop during treatment. Therefore, effective biomarkers are needed to monitor treatment effects and guide individualized treatment. Serum HER2 refers to the HER2 protein fragment present in the subject's serum. Serum HER2 levels may be more readily available than HER2 expression in tumor tissue and can be sampled multiple times during treatment, allowing real-time monitoring of disease progression and drug efficacy. If monitoring of serum HER2 levels accurately reflects tumor sensitivity to ADC drugs, it could be a valuable therapeutic monitoring tool.

In view of the excellent efficacy of ADC drugs in HER2-positive and low-expression breast cancer patients, this study intends to judge the therapeutic efficacy of breast cancer patients treated by anti-HER2-ADC drugs (such as T-DXd) through continuous detection of their serum HER2, providing a theoretical basis for the selection of clinical drug therapy.