<p>In healthy tissue, infiltrating <a href="https://en.wikipedia.org/wiki/Phagocyte" title="Phagocyte">phagocytes</a> are responsible for clearance of apoptotic or necrotic cellular debris, which includes cfDNA.<sup><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#cite_note-:0-9">[9]</a></sup> Levels of cfDNA in healthy patients is only present at low levels but higher levels of ctDNA in cancer patients can be detected. This possibly occurs due to inefficient immune cell infiltration to tumor sites, which reduces effective clearance of ctDNA from the bloodstream.<sup><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#cite_note-:0-9">[9]</a></sup></p>
<p> </p>
<p><input type="checkbox" /></p>
<h2>Contents</h2>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Methods">1Methods</a>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Pre-analytical_Considerations">1.1Pre-analytical Considerations</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Extraction_of_ctDNA">1.2Extraction of ctDNA</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Analysis_of_ctDNA">1.3Analysis of ctDNA</a>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Untargeted_approaches">1.3.1Untargeted approaches</a>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Digital_Karyotyping">1.3.1.1Digital Karyotyping</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Personalized_analysis_of_rearranged_ends_(PARE)">1.3.1.2Personalized analysis of rearranged ends (PARE)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#DNA_Methylation_and_Hydroxymethylation">1.3.1.3DNA Methylation and Hydroxymethylation</a></li>
</ul>
</li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Targeted_approaches">1.3.2Targeted approaches</a>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Digital_droplet_PCR_(ddPCR)">1.3.2.1Digital droplet PCR (ddPCR)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Beads,_Emulsification,_Amplification,_and_Magnetics_(BEAMing)">1.3.2.2Beads, Emulsification, Amplification, and Magnetics (BEAMing)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#CAncer_Personalized_Profiling_by_deep_Sequencing_(CAPP-Seq)">1.3.2.3CAncer Personalized Profiling by deep Sequencing (CAPP-Seq)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Tagged_AMplicon_deep_Sequencing_(TAM-Seq)">1.3.2.4Tagged AMplicon deep Sequencing (TAM-Seq)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Safe-Sequencing_(Safe-Seq)">1.3.2.5Safe-Sequencing (Safe-Seq)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Duplex_sequencing">1.3.2.6Duplex sequencing</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Integrated_Digital_Error_Suppression_(iDES)-enhanced_CAPP-Seq">1.3.2.7Integrated Digital Error Suppression (iDES)-enhanced CAPP-Seq</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Considerations">2Considerations</a>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#%E2%80%9CNormal%E2%80%9D_vs_tumor_DNA_detection">2.1“Normal” vs tumor DNA detection</a></li>
</ul>
</li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Research">3Research</a>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#ctDNA_in_cancer_screening">3.1ctDNA in cancer screening</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#ctDNA_in_cancer_monitoring">3.2ctDNA in cancer monitoring</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#ctDNA_as_a_prognostic_biomarker">3.3ctDNA as a prognostic biomarker</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Cancer_research">3.4Cancer research</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Challenges_for_implementation">3.5Challenges for implementation</a></li>
</ul>
</li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#See_also">4See also</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#References">5References</a></li>
<li><a href="https://en.wikipedia.org/wiki/Circulating_tumor_DNA#Further_reading">6Further reading</a></li>
</ul>
<h2>Methods</h2>