Breast cancer (BC) is the most commonly occurring type of cancer in women, being a major cancer-related cause of mortality worldwide. With the advancement in current therapeutic options, including hormone therapy and targeted therapies, there is a need for more accurate and less invasive options to monitor cancer progression in patients. Liquid biopsy has evolved rapidly, being able to detect small quantities of nucleic acids or cell-free DNA in the blood of BC patients. This method addresses three major issues of needle biopsy: firstly, it is more permissive by being less invasive and does not require needling the organs; secondly, it covers for the heterogeneous nature of the tumor of origin, which could lead to an otherwise inaccurate representation of the cancer-driving mutations; thirdly, it better represents the type of tumor that the primary tumor is going to evolve into before it starts to metastasize. This current review will address the current advancements in liquid biopsy in the context of BC, highlighting the pros and challenges.
