Hinrich’s Lab. 5.1.5 Circulating tumor DNA If sufficient plasma is available, select ed participant samples may be analyzed for circulating tumor DNA ( LTIB and NIH Core Facility ). Plasma DNA will be isolated with an automated purification system by Promega Corp using a system -attached bar -code reader to track samples and DNA products. The circulating tumor/HPV DNA will be quantified with a digital droplet PCR system from Bio -Rad to obtain precise quantification. This is just quantification by PCR.