Our STAR-FISH data showed that cells with PIK3CAH1047R are often present in untreated HER2+ breast tumors as minor subpopulations that increase in frequency after neoadjuvant chemotherapy with or without a HER2-targeted agent (Figure 1B), implying that mutant PIK3CA might play a role in therapeutic resistance (9). This evidence concerns the gene ERBB2 and breast neoplasm.