28P Rational thresholding of circulating tumor DNA copy number for early detection of disease progression in advanced metastatic breast cancer

Circulating tumor DNA (ctDNA) is promising as tumor-specific marker for progression surveillance in metastatic cancer. Our aim was to investigate the diagnostic power of ctDNA level disease breast cancer and propose rationally selected thresholds with clinical validity. This prospective single-center observational study conducted from July 1, 2019 December 2021, recruited 136 subjects sequencing their primary search PIKC3A variants amenable monitoring by droplet digital PCR. interim analysis reports on 265 on-treatment samples 19 PIK3CA H1047R or E545K. Subjects were sampled every 3-5 weeks median follow-up 85 (13-125) 14 (2-29) time points per subject. The outcome free survival. ROC logistic regression performed quantitative CA15-3 predict within 12 each sampling point. Likelihood ratios used rational selection result intervals. (AUC: 0.856; 95% CI 0.807-0.897)) outperformed 0.737; 0.663-0.801, P<0.001) weeks. below 10 mutant copies/mL reassuring while levels above 100 predicted 64% progressions earlier (IQR) lead (8-20) versus standard care. Logistic indicated complementary value presence two consecutive rises CA15-3, resulting a derived risk score AUC 0.908 (95% 0.854-0.947). A < 0.15 > 0.25 achieved 93% (95%CI 87%-96%) 82% 71%-90%) negative positive predictive values respectively, clinically informative 89% blood draws. Intensive shows validity improved has potential risk-informed scheduling