Circulating Cell-Free DNA and Cancer Therapy Monitoring: Methods and Potential

The monitoring of therapy during the treatment of cancer patients is currently assessed by the levels of circulating tumor cells or by PET/CT scans. Neither approach has the sensitivity or specificity to be very sure of the efficacy of the treatment. Moreover, PET/CT scans can be both comparatively expensive and produce low levels of radiation for the patient. The advent of the possibility of using circulating DNA released from the tumor permits (1) a possible early marker of the presence of the cancer, (2) an indication of the success of the primary treatment, (3) an indication of the early presence of possible metastasis, (4) a marker of the success of secondary subsequent treatment, (5) determining which patients can benefit from a particular treatment, and (6) offering a prognosis. These aspects will be discussed concerning the application of circulating tumor DNA analysis to the monitoring of cancer patients undergoing therapy.