Longitudinal ctDNA Monitoring in Older Women With ER+ Breast Cancer Who Forego Upfront Surgery in Favor of Primary Endocrine Therapy

Age is one of the most important risk factors for the development of breast cancer. Nearly a third of all breast cancer cases occur in older women (aged ≥ 70 years), with most cases being estrogen receptor-positive (ER+). Such tumours are unlikely to be the ultimate cause of death for older women, particularly when considering other comorbidities. Our group has recently shown that risk of breast cancer-related mortality is only around 3% for older women who forego upfront surgery and instead treated with primary endocrine monotherapy. However, with omission of surgery, surveillance for tumor growth or treatment failure is important but requires patients (and their caregivers) to have regular imaging and to see their oncology team every 3 months, which can be quite burdensome. Thus, this study employs a ctDNA surveillance scheme to monitor for potential tumor growth. Partnering with Natera, this study uses a bespoke, tumor-specific ctDNA assay (Signatera) to monitor for changes in ctDNA dynamics while the patient is on endocrine therapy.

This study is for patients who choose not to undergo primary surgical intervention and are managed medically on primary endocrine therapy (any endocrine therapy permitted). Patients will undergo Signatera testing at the time of regularly scheduled clinic follow-up visits and/or at the time of surveillance imaging, which will occur every 3-6 months. Patients will also be asked to complete regular surveys while participating in the study.