The ability to serially monitor tumor-derived cell-free DNA (cfDNA) brings with it the potential to measure response to anticancer therapies and detect minimal residual disease (MRD). This report describes a patient with HER2-positive metastatic breast cancer with an exceptional response to trastuzumab and nab-paclitaxel who remains in complete remission several years after cessation of therapy. Next-generation sequencing of the patient’s primary tumor tissue showed several mutations, including an oncogenic hotspot PIK3CA mutation. A sample of cfDNA was collected 6 years after her last therapy and then analyzed for mutant PIK3CA using digital PCR. No detectable mutations associated with the primary tumor were found despite assaying >10,000 genome equivalents, suggesting that the patient had achieved a molecular remission. Results of this case study suggest that serial monitoring of MRD using liquid biopsies could provide a useful method for individualizing treatment plans for patients with metastatic disease with extreme responses to therapy. However, large-scale clinical studies are needed to validate and implement these techniques for patient care.
Submitted August 2, 2019; accepted for publication November 25, 2019.
Author contributions:Study concept and design: All authors. Development of methodology: Hunter, Croessmann, Cravero, Shinn. Data acquisition: Hunter, Croessmann, Cravero, Shinn, Hurley. Data analysis and interpretation: All authors. Manuscript writing, review, and/or revision: All authors.
Disclosures: Dr. Park has disclosed that he is a scientific advisor for and has ownership interest in Loxo Oncology, and has received grant/research support from AbbVie, Pfizer, and Foundation Medicine, Inc. The remaining authors have not received any financial consideration from any person or organization to support the preparation, analysis, results, or discussion of this article.
Funding: Research reported in this publication was supported by the Breast Cancer Research Foundation (B.H.P.), the American Cancer Society (131356-RSG-17-160-01-CSM; P.J.H.), the Marcie & Ellen Foundation (N.H. and B.H.P.), and the NCI of the NIH under award numbers R01CA214494 (B.H.P.), R01CA194024 (S.C. and B.H.P.), and RO1CA211695 (P.J.H.).
Disclaimer: The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Correspondence: Ben Ho Park, MD, PhD, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, 2220 Pierce Avenue, PRB 777, Nashville, TN 37232. Email: email@example.com