Results from targeted sequencing of a panel of genes in both primary and metastatic HER2+ tumors revealed that there was a significant enrichment of mutations in the MAPK pathway in metastatic tumors indicating that in response to treatment with targeted therapy, a proportion of HER2+ cancers switch from PI3K/AKT signaling to MEK/ERK signaling [11]. The gene discussed is ERBB2; the disease is cancer.