Retrospective analyses of patients with advanced HER2-positive breast cancers treated with everolimus in the context of the BOLERO-1 and BOLERO-3 trials have suggested a correlation between patients with a hyperactive phosphatidylinositol-3-kinase (PI3K) pathway and PFS benefit,16 although such a correlation was not observed in patients with advanced HER2-negative breast cancers treated with everolimus in the context of the BOLERO-2 study.17 Here, ERBB2 is linked to breast cancer.