Abstract P4-01-01: Molecular residual disease detection with circulating tumor DNA analysis predicts relapse in patients with early stage breast cancer
Authors: Turner N , Garcia-Murillas I , Chopra N , Comino-Mendez I , Beaney M , Tovey H , Cutts R , Swift C , Kriplani D , Afentakis M , Hrebien S , Walsh G , Johnston S , Ring A , Russell S , Evans A , Skene A , Wheatley D , Dowsett M , Smith I 
Published: May 2019

Abstract
Background. Detection of circulating tumor DNA (ctDNA) after treatment of early stage breast cancer may identify molecular residual disease. In a prior proof-of-principle study we demonstrated that detection of ctDNA predicted relapse with high accuracy (Garcia-Murillas et al Science Trans Med 2015). We conducted an independent, prospective, multi-centre validation study.
Methods. In this validation study, a cohort of 170 early stage breast cancer patients were recruited from five hospitals into two prospective sample collection studies. Patients were scheduled to receive standard chemotherapy, surgery +/- radiotherapy, adjuvant endocrine therapy and HER2 antibodies as appropriate. Plasma samples were collected for ctDNA analysis at baseline, post-surgery, three monthly for the first year of follow-up, and six monthly thereafter and shipped to a central lab for processing. Using previously established criteria, tumor was sequenced to identify somatic mutations that were tracked by digital PCR in DNA extracted from 4mls of plasma at all available time points. Buffy coat DNA was analysed at all time-points to control for clonal haematopoesis of indeterminate potential (CHIP) detection. The primary endpoint was to compare invasive disease free survival between patients with and without detection of ctDNA after treatment. A combined analysis of this validation study, and the prior proof-of-principle study, was also conducted to analyse secondary endpoints.
Results. After tumor sequencing, 101 patients from the validation study had at least one mutation to track. At median 35.5 months follow-up, ctDNA was detected in plasma of 15.8% (16/101) patients. Detection of ctDNA strongly predicted relapse, hazard ratio 24.5 (95% CI 6.5 to 93.2, P&lt;0.001 time-dependent Cox model), and was predictive of relapse in all tumor subtypes.
In the combined analysis (N=144), lead-time between ctDNA detection and relapse was 10.7 months (95% CI 7.7-17.0). Six patients had a clinical relapse that was not detected by ctDNA prior to relapse. These patients had a distinct pattern of oligo-metastatic relapse, 3 patients with brain-only metastases (P=0.0068), 1 ovarian oligo-metastasis and 2 local disease recurrence. The level of ctDNA in baseline plasma, prior to treatment, was associated with tumor subtype, highest in triple negative breast cancer (P=0.0036).
Conclusion. Detection of ctDNA after treatment is associated with a high risk of future relapse in early-stage breast cancer. Prospective studies are required to assess the potential of molecular residual disease detection to guide adjuvant therapy.
Citation Format: Turner N, Garcia-Murillas I, Chopra N, Comino-Mendez I, Beaney M, Tovey H, Cutts R, Swift C, Kriplani D, Afentakis M, Hrebien S, Walsh G, Johnston S, Ring A, Russell S, Evans A, Skene A, Wheatley D, Dowsett M, Smith I. Molecular residual disease detection with circulating tumor DNA analysis predicts relapse in patients with early stage breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-01-01.