HER2 positive (HER2+) breast cancers account for 20-25% of breast cancers and are associated with higher rates of recurrence and brain metastases. However, in the past two decades, HER2 targeting therapies have drastically improved patient outcomes and most patients treated with stage I-III HER2+ breast cancer are cured. For patients with HER2+ metastatic breast cancer (mBC), the treatment paradigm is currently non-curative. While these treatments do extend the life of patients, treatment has to be given indefinitely, impacting patients’ quality of life. The treatments can cause significant adverse effects, are expensive, and require frequent visits for IV infusions. Recent studies have found that a significant subset of patients with HER2+ mBC do not experience growth or spread of their cancer at 8 to 10 years after treatment. Despite the fact that some patients have exceptional responses to treatment, there is no way to predict who may not need ongoing treatment. Minimal residual disease (MRD), microscopic residual tumor cells, may be a biomarker to determine exceptional response for HER2+ mBC and may guide the discontinuation of treatment if there is no detectable MRD. This phase II study will assess the discontinuation of HER2+ targeted therapy in patients with HER2+ mBC that have been free of disease progression for at least 3 years after starting therapy. Patients will be followed to see if they remain free of disease progression for a year after stopping treatment and the researchers will determine if there is a relationship between MRD at treatment discontinuation and MRD at one year.
Trial Registration: ClinicalTrials.gov Identifier: NCT05721248