[Abstract] Circulating tumor DNA (ctDNA), dormant disseminated tumor cells (DTCs) and recurrence outcomes in breast cancer survivors on the SURMOUNT Study

Abstract

Background: Recurrence after early-stage breast cancer (BC) is a challenge, occurring in ∼30% of patients (pts). Recurrences may arise from reactivation of disseminated tumor cells (DTCs) persisting in a dormant state after primary treatment. The presence of minimal residual disease (MRD) as bone marrow DTCs and/or circulating tumor DNA (ctDNA) in the blood increases the risk of BC recurrence/death. It remains unclear which pts with DTCs will have these reactivate or develop detectable ctDNA before clinical relapse. We evaluated the association and temporal relationship of ctDNA with DTCs in a population of high-risk BC survivors, and the relationship of these markers with subsequent metastatic recurrence.

Methods: “PENN SURMOUNT” is a single center, prospective, longitudinal cohort study examining MRD biomarkers among pts within 5 years (y) of BC diagnosis who completed all curative treatment except endocrine therapy. Eligible pts must have had: 1) TNBC, or 2) HER2+ or HR+ BC with positive LN and/or residual disease after neoadjuvant therapy, or 3) HR+ BC with a 21-gene Recurrence score >25 and/or high risk Mammaprint. Pts had annual bone marrow aspirate (BMA) for DTCs by immunohistochemistry (using methods of Naume et al.). DTC+ pts went on therapeutic trial; DTC- pts had up to 5y of annual BMA and blood testing. ctDNA was retrospectively assessed using the RaDaR assay, which targets pt-specific somatic mutations identified by whole-exome sequencing (WES) of primary tumor tissue.

Results: Of 184 pts enrolled from 2016 – 2021, 121 had tissue available; 114/121 (94%) had successful WES. A total of 338 plasma samples from 96 pts (median 2 timepoints each, range 1-12) have been successfully tested by RaDaR to date. Overall, ctDNA was detected in 11 samples from 9/96 pts (9.3%) with a median eVAF of 0.009% (range 0.002-0.084%). Two pts were ctDNA+ at baseline (BL), and 7 became positive on surveillance. 87/96 (90.6%) were ctDNA- across all timepoints. 34/96 pts (35%) were DTC+, either at BL (n=24, 25%) or after (n=10, 10%). Considering all timepoints, concordance was 64%. Of 34 ever-DTC+ pts, 4 (12%) were ctDNA+ (of whom 3/4 recurred) and 30 remained ctDNA- (with 1/30 who recurred). Among the 62 pts who remained DTC-, 5 (8%) were ctDNA+ (with 5/5 who recurred), and 57 remained ctDNA- (of whom 5/57 recurred). All ctDNA positivity in DTC+ pts occurred at the time of or after DTC positivity. Over median follow-up (f/u) of 65 months (m), BC recurrence occurred in 14/96 pts (15%), with 2 locoregional-only and 12 distant +/- locoregional recurrences (involving the bone, liver, lung/pleura, and brain); 8/14 pts (57%) were ctDNA+ prior to relapse. 7/12 (58%) with distant recurrences were ctDNA+ prior to metastatic diagnosis, at a median lead time of 15 m (range 0 – 25). Overall, ctDNA+ pts experienced a median lead time from ctDNA positivity to recurrence of 13 m (range 0 – 25). Only 1 of 9 ctDNA+ pts has not recurred; this pt was DTC+ and went on therapeutic trial, without evidence of recurrence over 20 m f/u. 30/34 DTC+ pts (89%) who went on therapeutic trial have not had ctDNA detected during f/u and have not recurred. Overall, ctDNA status was significantly associated with relapse (p<0.01), with a PPV of 89% and NPV of 93%. Of the 24 BL DTC+ pts, 2 became ctDNA+ at subsequent timepoints, an average of 18 m after DTC assessment, and both relapsed (3 and 5 m from ctDNA detection, respectively).

Conclusions: In this surveillance study of high-risk BC pts, DTC+ pts were identified who subsequently developed detectable ctDNA and clinical relapse. Where there were discordant results, the timing of DTC and ctDNA positivity revealed a window of opportunity for intervention. A strategy combining both markers for surveillance and intervention to prevent metastatic disease may be of value.

Nicholas J. Seewald

Assistant Professor of Biostatistics

Assistant Professor of Biostatistics at the University of Pennsyvlania Perelman School of Medicine