Abstract 2420: Evaluating circulating tumor DNA (ctDNA) as a prognostic biomarker utilizing a tissue-free epigenomic assay in early-stage triple negative breast cancer (TNBC)

Abstract Background: ctDNA has shown promise as a prognostic biomarker in early-stage solid tumors. Current breast cancer clinical guidelines do not recommend routine screening for metastatic disease outside of clinical features suggestive of disease recurrence. The detection of ctDNA may be a useful biomarker for the management of early-stage cancer patients to identify patients who are at high risk of recurrence. Methods: Patients with stage II or III TNBC undergoing neoadjuvant docetaxel and carboplatin chemotherapy on a clinical trial (NCT02124902) followed by surgery were included in this study. Blood samples were prospectively collected prior to, during, and after completion of neoadjuvant chemotherapy, post-surgery, and throughout pre-specified surveillance time points (every 6 months for 5 years). Plasma samples were analyzed using Guardant Reveal powered by Infinity, a tissue-free, multiomic assay that interrogates differentially methylated regions of DNA using an applied bioinformatics filter optimized to detect breast cancer DNA from non-cancerous cell-free DNA and estimate quantitative tumor fraction. Samples were sequenced and resulted blinded to the patients’ clinical data. Results: A total of 120 patients with evaluable plasma samples were included in this study. At baseline prior to chemotherapy, ctDNA was detected in 75% (54/72) of patients. Baseline ctDNA detection was higher in node-positive cancers (100%; 29/29) versus node-negative cancers (58%; 25/43; p<0.0001). ctDNA quantity was higher in node-positive cancers (p<0.0001), and in stage III versus stage II disease (p=0.0179). During surveillance follow-up, the sensitivity for detecting any distant metastatic recurrence was 71% (5/7). Among patients with samples drawn within one year of recurrence, the sensitivity for detecting distant recurrence was 83% (5/6) with a sample-level specificity of 98% (186/190) and a patient-level specificity of 94% (63/67). ctDNA detection prior to recurrence had a median lead time of 5.0 months (range, 4.6-5.6). Notably, the detection of ctDNA during follow-up was associated with worse recurrence-free (HR 23.3, 95% CI 2.70-201, p<0.0001) and distant-recurrence free survival (HR 29.3, 95% CI 1.86-461, p<0.0001). Conclusions: ctDNA is detected with a tissue-free MRD assay with high sensitivity and specificity for distant recurrence in early-stage TNBC. Furthermore, the presence of ctDNA during follow-up is a prognostic indicator. Additional prospective studies are needed to assess the clinical utility of ctDNA monitoring in early-stage TNBC. Citation Format: Foluso O. Ademuyiwa, Cynthia X. Ma, Katherine Weilbaecher, Rama Suresh, Lindsay Peterson, Ron Bose, Nusayba Bagegni, Caron E. Rigden, Ashley Frith, Katherine Clifton, Andrew Davis, Derek Dustin, Mingyang Cai. Evaluating circulating tumor DNA (ctDNA) as a prognostic biomarker utilizing a tissue-free epigenomic assay in early-stage triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2420.