Liquid biopsy for cancer: Review and implications for the radiologist

Imaging and image-guided procedures play an imperative role in the screening, diagnosis, and surveillance of cancer. Although emerging imaging techniques now enable more precise molecular characterization of tumors, multigenetic tumor profiling for targeted therapeutic selection remains limited to direct tissue acquisition. Even in the context of targeted therapy, tumors adapt to acquire resistance. This necessitates serial monitoring, traditionally through tissue acquisition, to identify the molecular mechanism of resistance and to guide second-line therapy. An alternative to tissue acquisition is the collection of circulating tumor markers such as cell-free nucleic acids and circulating tumor cells in the peripheral blood. This noninvasive diagnostic approach is referred to as the liquid biopsy. The liquid biopsy is currently used clinically for therapeutic guidance when tissue acquisition is impossible or when the specimen is inadequate. It is also being studied in the context of screening, diagnosis, and surveillance. As cancer treatment continues to move toward a focus on precision medicine, this developing technology may alter and/or augment the role of imaging in the management of cancer. This review aims to outline the use of liquid biopsy in cancer and its potential impact on diagnostic imaging and image-guided procedures.