PIK3CA mutations are reported in 18%–40% of breast cancers (Kalinsky et al. 2009; Cizkova et al. 2012; Harle et al. 2013), most frequently in exon 9 and 20 (Campbell et al. 2004; Samuels et al. 2004). The gene discussed is PIK3CA; the disease is breast carcinoma.