ERBB2 and breast cancer: Against this background, the present study had three main objectives: (i) to quantify the concordance of ER, PR, HER2, and Ki-67 between diagnostic core biopsies and corresponding surgical specimens in a real-world breast cancer cohort; (ii) to measure the frequency and direction of clinically actionable reclassification of these biomarkers; and (iii) to identify treatment contexts—particularly neoadjuvant chemotherapy versus upfront surgery—in which routine post-surgical IHC reassessment is most likely to provide added value for systemic therapy decisions.