In breast cancer, we observed similar frequencies of altered genes (Pearson’s r = 0.97) in both cfDNA and tumor biopsies, including mutations in TP53, ESR1, and PIK3CA, amplifications of MYC, CCND1, ERBB2, PIK3CA, and losses of ATM and RB1 (Fig. 3a). Here, ESR1 is linked to breast cancer.