ERBB2 and neoplasm: A similar discordance rate was reported (38.0%), mostly represented by ERBB2-zero disease switching to ERBB2-low disease (36.4% of the ERBB2-zero cohort) and ERBB2-low disease to ERBB2-zero disease (41.2% of the ERBB2-low cohort).18,19 The discrepancy in ERBB2 expression between primary and metastatic disease may result from genetic drift during tumor progression,20 intratumoral heterogeneity,21 and selective pressure of therapies with potential upregulation of ERBB2 expression.22,23 This instability is important to consider if dedicated drugs are approved in the near future.