Fig. 1 | npj Precision Oncology

Fig. 1

From: The potential of liquid biopsies for the early detection of cancer

Fig. 1

Plasma DNA diagnostics in physiologic and pathologic conditions. a Pregnancy is a physiologic scenario which results in a relatively constant and reproducible, i.e., similar in different pregnancies, release of fetal or placental DNA into the circulation. Hence, diagnostic procedures are easy to standardize. The graph at the bottom indicates the fetal plasma DNA fraction as a function of gestational age and shows a positive correlation. In the majority of pregnancies fetal fractions of more than 4%, which is considered to represent a threshold for reliable non-invasive prenatal testing, are already present at 10th week of pregnancy (graph adapted from ref. 126). b In contrast, cancer is a pathologic process, which is often heterogeneous (various clones within the primary tumor are depicted in different colors and furthermore metastatic sites, which also contribute) including multiple parameters, e.g., the microenvironment (indicated here by tumor infiltrating lymphocytes) and access to blood vessels, which affect the release of tumor DNA and which may cause significant variation from one patient to the next. At the bottom, average ctDNA levels for tumor stages I to IV are depicted. However, as indicated by the bars, these values may vary tremendously for each stage (graph adapted from ref. 42) and are frequently below 4% required for NIPT. For clarity, we only show DNA fragments in the blood vessels, although other factors, e.g., extracellular vesicles, or modifications of the DNA either by epigenetic changes or alterations in the nucleic acid sequence can also be detected in the systematic circulation

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