According to the circulating tumor DNA (ctDNA) sequencing results, about 50% of HR-positive metastatic breast cancers (MBCs) have PIK3CA missense mutations; 10-30% of metastatic triple-negative breast cancers (TNBC) and HER2-positive breast cancers have PIK3CA missense mutations [5]. The gene discussed is PIK3CA; the disease is maternal uniparental disomy of chromosome 20.