To estimate the inherent variability within clinical histopathology and to determine a consensus score for each BC biomarker for classifier training, a comprehensive histopathologic analysis was performed for 405 patient breast tumors with three readings of up to two independent stains for the five conventional biomarkers: ER, PgR, HER2, Ki67, and NHG (Fig 1). The gene discussed is ESR1; the disease is breast cancer.