ERBB2 and breast cancer: Distribution of ctDNA TF in BO-MBC versus non-BO MBC was similar by MBC receptor subtypes (Fig. 2C–E), with hormone receptor-positive/HER2-negative breast cancer reflecting a slightly higher proportion of samples with TF > 1% in non-BO MBC (50% TF > 1% for BO-MBC vs. 61.3% for non-BO MBC; P = 0.03).