- Carcinoembryonic antigen (CEA) and CA 15-3 serve as biomarkers in the two prevalent cancers of the colon and breast, respectively. However, their sensitivity for screening is tow. Circulating DNA has been suggested as a potential marker. We developed a fluorometric method which enables an easy, fast and reliable DNA measurement. This manuscript presents the results of our experiments to evaluate the significance of DNA measurements in breast and colon patients. Patients who had been diagnosed with early stages of colon or breast cancer were recruited into a prospective study. Blood samples were withdrawn for the determination of CEA, CA 15-3 (according to the type of cancer) and circulating DNA concentrations prior to any therapeutic intervention. Control DNA Levels were determined in blood samples of healthy volunteers. Mean circulating DNA in patients with colon cancer was higher than in control subjects [798+409 ng/ml vs. 308 +/- 256 ng/ml, p<0.0001. High DNA concentrations were identified in 40% of colon patients compared with 28% with increased CEA levels. Mean DNA levels among breast cancer patients was higher than the control group [1060 +/- 670.9 ng/mt vs. 376.2 +/- 244.1 ng/ml, p=0.0001]. High DNA concentrations were identified in 53% of breast cancer patients compared with 9% with increased CA 15-3 levels. A novel simple, rapid, cheap and reliable fluoroscopic method was used to determine circulating DNA levels in the blood of breast and colon cancer patients. Increased DNA concentrations were found in the blood of early cancer patients. This method demonstrates a better sensitivity compared with the traditional markers.