In total, 46% (6 of 13) of the patient-matched tumor-PDX-O pairs with a ERBB2 mutation or amplification detected in either, had discordance of ERBB2 mutational status, results consistent with the high frequency of ERBB2 mutational discordance observed in our analysis of primary–metastasis tumor pairs27. The gene discussed is ERBB2; the disease is neoplasm.