New analysis reveals major gaps in US TNBC trial access, leaving rural and minority communities with fewer treatment options and research opportunities.
Resources|Articles|August 17, 2026
The Oncologist's Guide to Biomarker Testing in Breast Cancer
Author(s)Sabrina Serani
A guide to breast cancer biomarker testing, from ER/PR and HER2-low status to PIK3CA, AKT1, and ESR1 mutations across diagnosis and disease progression.
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Biomarker testing shapes nearly every treatment decision in breast cancer, from initial subtyping through resistance monitoring at progression. Hormone receptor and HER2 status remain the foundation of first-line treatment selection, but the biomarker landscape has expanded considerably—HER2-low and HER2-ultralow classifications now extend antibody-drug conjugate eligibility beyond traditionally HER2-negative disease, while PIK3CA, AKT1, and ESR1 testing increasingly guide therapy selection and switching in the hormone receptor-positive, metastatic setting. This slideshow reviews the biomarkers oncologists should be testing for across the diagnosis-to-progression continuum, along with current ASCO and ASCO/CAP testing recommendations.
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