Consistent with previous studies, luminal breast cancers exhibit a greater frequency of HER2-low tumors in contrast to TNBC.13,28–30 The analysis of ctDNA from 1071 MBC patients revealed that among the 488 HER2-low MBC patients, TP53, PIK3CA, and ESR1 exhibited the highest frequency of mutations. The gene discussed is PIK3CA; the disease is breast cancer.