Cell-Free DNA (cfDNA)

Type

Method / Biomarker

Description

Cell-free DNA (cfDNA) refers to fragmented DNA circulating in the bloodstream, primarily released by apoptotic cells. The majority of cfDNA in healthy individuals originates from hematopoietic cells. cfDNA fragments are predominantly 167 bp in length, corresponding to DNA wrapped around a single nucleosome. In cancer patients, a fraction of cfDNA is tumor-derived (ctDNA); the ratio varies from <0.01% in early-stage disease to >90% in advanced metastatic disease. cfDNA is the broader category; ctDNA is the clinically relevant tumor-specific subset.

Key metrics

• Typical fragment size: 167 bp (nucleosome unit)
• Half-life: minutes to 2 hours
• Primary source: hematopoietic cells (apoptotic)

Wiki sources

• cfdna-vs-ctdna-explained — cfDNA vs ctDNA distinction and clinical applications
• abbosh2017-ctdna-tracerx — cfDNA as the substrate for ctDNA detection in NSCLC
• stejskal2023-ctdna-biology-review — ctDNA biology and release mechanisms