Approximately 40% of estrogen receptor-positive (ER+)/HER2-breast carcinomas have mutations in the PIK3CA gene, leading to hyperactivation of the alpha isoform (p110α) of phosphatidylinositol-3-kinase (PI3K) (Cancer Genome Atlas Network, 2012; Goncalves et al., 2018; Mollon et al., 2018). The gene discussed is ERBB2; the disease is breast carcinoma.