Prevalence of PIK3CA mutations in pBC and mBC: (A) pBC, BASIS cohort; (B) mBC, CPCT-02 cohort; (C) pBC, Razavi cohort; and (D) mBC, Razavi cohort. The Fisher's exact test was used to determine differences between the fraction of APOBC mutations between single and dual PIK3CA mutations. For patients with dual PIK3CA mutations, at least one mutation occurring at an APOBEC site was required to be classified as ‘APOBEC site’. APOBEC, Apolipoprotein B mRNA-Editing Catalytic Polypeptide-like; mBC, metastatic breast cancer; pBC, primary breast cancer.