The ERBB2/CDH1/ESR1 observations were consistent with prior observations in metastatic breast cancer in which acquired ERBB2 and ESR1 resistance mutations were mutually exclusive, with ERBB2 resistance mutations co-occurring with CDH1 loss-of-function (LOF) mutations, suggesting enrichment in lobular breast cancers (23). This evidence concerns the gene CDH1 and Hereditary breast cancer.