The phosphatidylinositol 3-kinase (PI3K) pathway is frequently activated in breast cancers due to (i) amplification of ERBB2, an oncogene that stimulates the PI3K pathway and (ii) activating mutations of the PI3K catalytic subunit, PIK3CA (Koboldt et al., 2012). The gene discussed is PIK3CA; the disease is breast cancer.