BACKGROUND

Circulating tumour DNA (ctDNA)-based detection of molecular residual disease (MRD) presents a strategy to identify patients at high risk of relapse. In this article, we profile early breast cancer patients with an ultrasensitive, whole genome sequencing (WGS)-based, tumour-informed ctDNA platform.

MATERIALS AND METHODS

We analysed 617 plasma samples (median 8, range 2-14) from 78 patients (23 triple-negative breast cancer, 35 human epidermal growth factor receptor 2-positive, 18 hormone receptor-positive, and 2 unknown). Samples were collected at diagnosis before therapy, cycle 2 of neoadjuvant chemotherapy, post-surgery after neoad'juvant therapy if administered, every 3 months during the first year, and every 6 months thereafter. Plasma DNA was analysed using the NeXT Personal MRD platform, a tumour-informed WGS approach to produce personalized ctDNA sequencing panels tracking a median of 1451 variants per patient. MRD detection was correlated with clinical outcomes.

RESULTS

ctDNA was detected at levels ranging from 2.19 parts per million (PPM) to 204 900 PPM (median 405 PPM), with 39% of all ctDNA detections in the ultra-low range <100 PPM. Of patients with samples at diagnosis, 98% (49/50) had ctDNA detected before treatment. At a median follow-up of 76 months (range 5-118 months), detection of ctDNA was associated with high risk of future relapse (P < 0.0001; log-rank test) and shortened overall survival (P < 0.0001) with a median lead time from ctDNA detection to clinical relapse of 15 months (range 0.9-61.5 months). MRD was identified in 100% (11/11) of patients who relapsed, with a median level of ctDNA at first MRD detection of 13.1 PPM. No ctDNA-undetected patients relapsed throughout follow-up (64/64). Comparison with exome-powered MRD detection assays showed improved sensitivity and lead time.

CONCLUSIONS

A whole genome-powered MRD assay detected breast cancer relapse with a long lead time over clinical relapse, and was strongly associated with relapse-free survival. Rates of ctDNA detection at diagnosis were higher than those reported with exome-based tumour-informed assays.