ESR1 and cancer: Lastly, WES of ctDNA can consistently capture cancer-related genes of interest [27] that were present in tumor tissues (Fig 4), including ESR1, KRAS, PIK3CA, PIK3R1, FAT1, MED12, and MUC16 for breast cancer, APC, CASP8, TP53, KRAS, CDH11, GRIN2A, ASXL1 and MYH9 for gastrointestinal cancer, and PSIP1, RSPO2, and SF3B1 for melanoma/liver cancer.