However, given role of PIK3CA_p.I391M and PIK3CA_ p.E110K in several malignancies [27–29], we consider this third option less likely (especially given the absence of both alterations in participant 4 and 5's sequenced BC) and propose that the variants’ presence in the circulation still provides strong evidence for ctDNA in these participants. This evidence concerns the gene PIK3CA and breast cancer.