Du, T., Lin, M., Liang, G., Wang, Y., Wu, H., Li, N., Zhao, Z., Sun, L., Tang, J. (2026). Optimizing the ER cutoff: Using ER≥50% to define a distinct HER2+ subgroup characterized by low pCR rates, ADC resistance, and CDK4 dependency.. Journal of Clinical Oncology. https://doi.org/10.1200/jco.2026.44.16_suppl.e12646