A malignant tumor is a bustling metropolis populated by many different kinds of cancer cells, where each one is different from the rest and can act differently within the same tumor.
The two blood tests CA 15.3 and CEA have been in clinical use for decades to monitor breast cancer and colorectal cancer recurrence respectively. Both tests are known to be severely limited in their effectiveness. They only apply to 25% of the disease population and recognize patients mostly in the later stages of disease.
Recent liquid biopsy tests are based on tiny circulating tumor DNA (ctDNA) fragments in the blood. These tests suffer from a lack of sensitivity, specificity and other technical issues. Abundant literature from the public domain that highlights the clinical limitations in the utility of ctDNA. Some limitations include:
Recommending therapeutic interventions to cancer patients, based on the genetics of heterogeneous cancer cells that change constantly begs the question of the real clinical value of ctDNA!
Art Courtesy of Michael Murphy