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The risk of recurrence remains after 5 years in HR-positive breast cancer. The role of assessing minimal residual disease (MRD) using circulating tumor DNA (ctDNA), and the ability to predict distant recurrences after 5 years of original diagnosis was assessed in a study by Lipsyc-Sharf et al in the .

ctDNA was studied in 103 high-risk HR+ breast cancer patients and was detected approximately 1 year prior to clinical presentation with distant metastases. Recurrence-free survival was worse for MRD-positive patients compared with those who were MRD negative.

The study also identified that 10% of the patients had MRD; however, the study population is small (n=83), and larger studies would be needed to confirm the prevalence rates of MRD in this population.

The ability to use ctDNA as a "tumor marker" for surveillance is an exciting concept. However, the role of ctDNA in routine clinical practice remains undefined as we have not yet identified a mechanism to use the test to alter the outcomes of the disease. This is important as in clinical practice we would have to offer an intervention if a positive test is detected; otherwise, we risk harming patients with information that can provoke anxiety.

Studies are currently underway looking into if initiation of therapy with CDK4/6 inhibitors earlier at the detection of MRD, rather than later at presentation with distant metastases on imaging, would improve outcomes. The results of these studies would be important to know prior to incorporating ctDNA into clinical practice, which for now remains a research tool.

Rosana Gnanajothy, MD, is Assistant Professor of Hematology and Medical Oncology at Winship Cancer Institute of Emory University in Atlanta.

Read the study here and an interview about it here.