Liquid Biopsy in Breast Cancer: A Focused Review.

CONTEXT.—: The role of liquid biopsy in cancer management has been gaining increased prominence in the past decade, with well-defined clinical applications now being established in lung cancer. Recently, the US Food and Drug Administration also approved the Therascreen PIK3CA RGQ polymerase chain reaction assay as a companion diagnostic assay to detect PIK3CA mutations in breast cancer for both tissue and liquid biopsies, bringing the role of liquid biopsy in breast cancer management to the fore. Its utility in other aspects of breast cancer, however, is yet to be clearly defined. OBJECTIVE.—: To review the studies that looked at liquid biopsies in breast cancer and examine their potential for clinical application in the areas of early diagnosis, prognostication, monitoring disease response, detecting minimal residual disease, and predicting risk of progression or relapse. We focus mainly on circulating tumor cells and circulating tumor DNA. DATA SOURCES.—: Peer-reviewed articles in PubMed. CONCLUSIONS.—: Liquid biopsies in breast cancers have yielded promising results, especially in the areas of monitoring treatment response and predicting disease progression or relapse. With further study, and hopefully coupled with continued improvements in technologies that isolate tumor-derived materials, liquid biopsies may go on to play a greater role in the breast cancer clinic.