ERBB2 and neoplasm: Whereas none of the conventional univariable biomarkers (tumor size T, node status N, histological grade, ER, PR, HER2, or Nottingham Prognostic Index) were associated with outcome using logistic regression in this limited patient series, ctDNA level was a significant predictor of poor disease-free survival (odds ratio (OR) of 2.1 for each doubling of ctDNA level, 95% CI 1.3 to infinity; P = 0.02; Fig5E) as well as poor overall survival (OR 1.3 for each ctDNA doubling, 95% CI 1.03–1.9; P = 0.04; Fig5F) (Supplementary Table S7).