Dr. Tolaney on the Advantages of ctDNA Versus Tissue Biopsy in Breast Cancer

Sara M. Tolaney, MD, MPH, associate director, Susan F. Smith’s Center for Women’s Cancers, director, Clinical Trials, Breast Oncology, and senior physician, Dana-Farber Cancer Institute, and assistant professor of medicine, Harvard Medical School, discusses the advantages of circulating tumor DNA (ctDNA) versus tissue biopsy in breast cancer.

At the 2019 AACR Annual Meeting, Tolaney and fellow investigators presented data regarding the frequency of PIK3CA and ESR1 mutations in patients enrolled in the phase III MONARCH 2 trial. Approximately 40% of patients who underwent ctDNA testing had PIK3CA mutations. A similar prevalence of PIK3CA mutations was identified with formalin-fixed paraffin-embedded (FFPE) tissue. However, 60% and 4% of ESR1 mutations were identified with ctDNA compared with FFPE tissue, respectively.

Compared with FFPE tissue, ctDNA is easier to collect and track over time, says Tolaney. ctDNA may also have increased sensitivity compared with tissue-based samples due to tumor heterogeneity. As such, the hope is that ctDNA could be performed more routinely in the future in patients with metastatic disease, concludes Tolaney.