In estrogen receptor–positive, HER2-negative early breast cancer, disease recurrence may occur many years after initial diagnosis despite completion of standard adjuvant therapy. Circulating tumor DNA (ctDNA) monitoring has emerged as a potential approach to detect molecular relapse, defined as the presence of tumor-derived DNA in plasma in the absence of clinical or radiologic evidence of disease. Detection of minimal residual disease using plasma-based assays may identify patients at particularly high risk of recurrence, but whether ctDNA-guided therapeutic intervention can improve clinical outcomes remains under investigation.
Read more: ctDNA in Breast Cancer
The DARE Trial
The DARE trial (NCT04567420) is a prospective, multicenter, randomized phase II study designed to evaluate whether circulating tumor DNA–guided intervention at molecular relapse can improve outcomes in patients with high-risk estrogen receptor–positive, HER2-negative early breast cancer. The study investigates whether initiating second-line adjuvant therapy at the time of ctDNA detection—before radiologic evidence of metastatic disease emerges—can improve patient outcomes.
Study Population and Methods
Patients with high-risk ER-positive, HER2-negative breast cancer who have completed or are currently receiving adjuvant endocrine therapy with an aromatase inhibitor or tamoxifen and are within 7 years of definitive breast surgery are eligible for ctDNA surveillance. High-risk disease is defined by clinical or genomic features, including an estimated recurrence risk >15% according to validated models (PREDICT, RSPC, CTS5), more than four positive axillary lymph nodes, or other adverse clinicopathologic characteristics such as larger primary tumor size or node-positive, high-grade disease. Patients may also qualify based on high molecular risk, including Oncotype DX recurrence score >26, MammaPrint high-risk classification, EndoPredict score >4, or Prosigna score >60. Eligible patients undergo serial ctDNA monitoring every 6 months using a tumor-informed assay (Signatera; Natera, Inc.).
Randomization and Treatment Arms
Patients who test ctDNA-positive during surveillance undergo systemic staging with CT imaging of the chest, abdomen, and pelvis to assess for evidence of metastatic disease. Those without radiologic evidence of recurrence are randomized 1:1 to receive either palbociclib plus fulvestrant for up to two years or to continue standard adjuvant endocrine therapy. Premenopausal and perimenopausal patients assigned to the palbociclib–fulvestrant arm receive concurrent ovarian suppression with a GnRH analogue. Patients in both study arms may continue adjuvant bisphosphonate therapy, and those in the control arm may switch between different aromatase inhibitors based on tolerance. The planned maximum treatment duration in the investigational arm is two years, after which patients may resume their originally planned adjuvant endocrine therapy.
Interim Results
Interim results from the surveillance cohort were reported in a prospective analysis of the DARE trial. Among 552 patients with tumor tissue submitted for assay design, 494 had ctDNA results available, of whom 432 tested ctDNA-negative, with a median screening duration of 27.4 months. During follow-up, four ctDNA-negative patients experienced recurrence, corresponding to a negative predictive value of 100% at 6 months and 99% at 12 months after testing. Among patients who developed ctDNA positivity without radiologic evidence of metastatic disease, 40 patients were randomized to the interventional phase of the study. ctDNA clearance was higher in the palbociclib plus fulvestrant arm (63%) than in the standard endocrine therapy arm (22%). Early on-treatment ctDNA dynamics were associated with risk of recurrence, with rising ctDNA levels during the first months of therapy identifying patients more likely to develop recurrence compared with those whose ctDNA levels declined after treatment initiation.
Investigator Perspective
Commenting on the broader clinical context of ctDNA monitoring in early breast cancer, Lajos Pusztai, MD, DPhil, an investigator of the DARE study, noted:
Lajos Pusztai, MD, DPhil — Yale Cancer Center, Yale School of Medicine.
“There are many different potential clinical uses of ctDNA monitoring during the course of treatment for early stage disease, stage I-III breast cancer. It is important to distinguish between these clinical niches, which are illustrated in the figure below, because they represent different degrees of maturity in terms of supportive data, and also different degrees of urgency.”
“In some of the above niches there are proven alternative tests. For example to assess response to neoadjuvant therapy one can use imaging. To estimate prognosis post neoadjuvant chemotherapy one can use the extent of the residual cancer. In these instances, ctDNA needs to show added value by increasing the accuracy or precision when added to the older tools to predict a particular outcome.
The DARE study, along with a few other ongoing and planned trials, is unique because it explores an entirely new clinical niche, serial ctDNA monitoring to detect molecular relapse. Molecular relapse is detectable ctDNA in the plasma without any clinical evidence of recurrence. An overwhelming amount of data support that several different ctDNA assay can detect molecular relapse 8-18 months before cancer recurrence becomes clinically obvious through imaging or symptoms. The DARE trial tests if starting a new treatment at the time of molecular relapse, a second-line adjuvant therapy, could avoid in some patients a clinical recurrence and ultimately further improve cure rates by treating an impending recurrence before it becomes clinically apparent.
If this strategy works it would be hugely important because it could address a very inconvenient truth. Most breast cancer death is from low risk stage I-II breast cancers (Marczyk M, et al. Trends in breast cancer–specific death by clinical stage at diagnoses between 2000 and 2017. Journal of the National Cancer Institute. 2025 Feb;117(2):287-95). This is because there are so many of these patients, many more than stage III breast cancers. While a 5% personal risk of recurrence is considered low, it still implies that 1 in 20 patients experience a recurrence. Currently, the only reasonable strategy that could possibly reduce death from early stage low risk breast cancer is the DARE strategy, IF IT WORKS.”
The ongoing DARE trial will determine whether ctDNA-guided treatment at molecular relapse can improve outcomes in early breast cancer.
Written by Marine Rushanyan, MD