Abstract Addition of HER2-targeted agents to neoadjuvant chemotherapy has dramatically improved pathological complete response (pCR) rates in early stage Human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Still, up to 50% of patients have residual disease following treatment and biomarkers predictive of response are urgently needed. We performed spatial proteomic characterization using NanoString GeoMX Digital Spatial Profiling (DSP) of 122 samples from 57 HER2-positive breast tumors from the neoadjuvant TRIO-US B07 clinical trial (discovery cohort, n=28; validation cohort, n=29) sampled pre-treatment, after 14-21 days of HER2-targeted therapy and at surgery. In situ quantification of 40 tumor and immune proteins across multiple pancytokeratin-enriched regions per sample revealed that treatment results in decreased HER2 signaling and increased immune infiltration after several weeks of therapy. These changes were more dramatic in tumors that ultimately undergo pCR, and a classifier trained to predict pCR using on-treatment and pre-treatment DSP protein levels had a cross-validation mean Area Under the Receiver Operating Characteristics (AUROC) of 0.733 in the discovery cohort and validated in an independent cohort (AUROC = 0.725). Thus, we demonstrate robust stratification of sensitive tumors early during neoadjuvant HER2-targeted therapy using a multiplex spatial proteomic biomarker with implications for tailoring subsequent therapy.
Rod Jackson (2000) studied this question.