Circulating tumor DNA (ctDNA) is fragmented DNA from your tumor cells found in the blood. When tumor cells die, they release ctDNA into the bloodstream where it circulates. Blood can be tested for the presence of ctDNA or the amount of ctDNA, and the ctDNA in blood can be isolated and tested for mutations. Testing of ctDNA can be used to., As the cancer grows, minuscule fragments of cancer cells, known as circulating tumor DNA (ctDNA), begin to shed into the bloodstream. Although that idea might make you shiver, the use of ctDNA in blood tests is drastically changing how cancer is detected, treated, and monitored., Known as a liquid biopsy, we can learn what’s going on inside a patient’s body by examining circulating tumor DNA (ctDNA) or circulating tumor cells captured with a blood draw. Anthony Lucci, M.D., shares more on these tests, including how they work, their current limitations and the hope for their future. What is ctDNA testing?, Advances in technology have made it possible to extract ctDNA from a blood sample, measure it, and analyze it for genetic abnormalities. These tests, known as liquid biopsies, are being studied for their potential in guiding cancer care. How does ctDNA get into the bloodstream?, Circulating tumor DNA (ctDNA) is 150–200-base-pair fragments of DNA, which originate from cancer cells and are present in the bloodstream or other body fluids. How is ctDNA different than cfDNA?, 1. ctDNA tests look for minimal residual disease. Even after a patient finishes treatment for cancer, some cancer cells can still be left behind, circulating in the patient’s blood. These tiny bits are called minimal residual disease, or MRD. ctDNA tests work by looking for MRD in a patient’s blood..