Spatial determinants of antibody-drug conjugate SHR-A1811 efficacy in neoadjuvant treatment for HER2-positive breast cancer.

Selecting optimal candidates for next-generation anti-human epidermal growth factor receptor 2 (HER2) antibody-drug conjugates (ADCs) remains challenging. We conduct a prespecified translational study to identify treatment biomarkers in SHR-A1811-treated HER2-positive breast cancer patients from the phase 2 neoadjuvant FASCINATE-N trial using DNA and RNA sequencing, computational pathology, and single-cell in situ spatial imaging. In the hormone receptor (HR)-negative subgroup, a higher proportion and more infiltration of immune cells (i.e., tumor-infiltrating lymphocytes [TILs]), particularly cytotoxic T cells, are associated with better treatment responses. In the HR-positive subgroup, the closeness and aggregation of HER2-strong-positive tumor cells, as opposed to a uniform distribution, are linked to a lower response rate and HER2 luminal-like (HER2-LUM) subtype, which more closely resembles HR+/HER2- breast cancer. In addition, we develop a clinically practical predictive model capable of predicting neoadjuvant treatment responses to SHR-A1811 and other novel ADCs based on clinicopathological characteristics and pathological images.