Tissue-Free vs Tumor-Informed ctDNA Assays for Molecular Residual Disease Detection in Early Triple Negative Breast Cancer.

Abstract

Molecular residual disease (MRD) detection has potential to transform the selection of adjuvant therapy. Most evidence is from tumor-informed assays. Tissue-free assays not requiring sequencing of the primary tumor may simplify workflows if they offer accuracy similar to that of tumor-informed assays. To evaluate tissue-free circulating tumor DNA (ctDNA) analysis in patients with triple negative breast cancer (TNBC) and compare the tissue-free assay with tumor-informed assay results. This was a prognostic and exploratory analysis of patients with TNBC at moderate to high risk of recurrence who were participating in the ctDNA surveillance period of c-TRAK TN, a multicenter phase 2 clinical study. Plasma samples were collected from participants every 3 months for up to 2 years after the completion of adjuvant therapy and analyzed prospectively with digital polymerase chain reaction (dPCR). Data for the analysis were from a database lock on September 28, 2021, with subsequent follow-up through January 18, 2023. Data were analyzed from July 2025 to May 2026. Tissue-free assay leverages cancer differential methylation patterns to detect ctDNA. Recurrence-free survival by tissue-free ctDNA detection status. Comparison between tissue-free ctDNA detection and both dPCR and whole-exome sequencing-powered multivariant tumor-informed assays. The analysis included 1026 plasma samples from 159 patients (mean [SD; range] age, 51.4 [11.4; 25.0-78.0] years; 159 females [100%]). The tissue-free assay detected ctDNA in 54 patients (34.0%), with detection strongly associated with risk of recurrence (HR, 27.2; 95% CI, 13.7-54.2; P < .001). Among patients with ctDNA detected by both the tissue-free assay and dPCR (42 patients [26%]), tissue-free detection occurred at an earlier time point in 14 patients (33.3%); dPCR detection occurred before tissue-free detection in no patients. Median lead time to recurrence was 7.9 (95% CI, 6.1-10.5) months for tissue-free vs 5.8 (95% CI, 3.3-10.0) months for dPCR (HR, 0.57; 95% CI, 0.34-0.95; P = .03). Concordance between tissue-free and multivariant tumor-informed assays was good. Among patients detected by both assays (41 of 133), 12 of 41 (29.3%) had ctDNA detected earlier by multivariant tumor-informed assay with 1 (2.4%) earlier by the tissue-free assay. Median lead times to recurrence were 7.6 (95% CI, 4.6-10.5) months with tissue-free and 7.1 (95% CI, 5.7-10.0) months with multivariant tumor-informed assay (HR, 1.46; 95% CI, 0.87-2.44; P = .15). In this prognostic study, tissue-free ctDNA detection during surveillance was strongly prognostic for recurrence in patients with TNBC. Comparable lead times between the tissue-free and multivariant tumor-informed assays support tissue-free MRD detection in a clinical trial setting, permitting ctDNA testing when tissue is not available.