> For the complete documentation index, see [llms.txt](https://knowledge.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://knowledge.illumina.com/library-preparation/trusight-oncology-tumor/library-preparation-trusight-oncology-tumor-faq-list/000002892.md).

# TruSight Oncology 500 ctDNA liquid biopsy information

TruSight Oncology 500 ctDNA (TSO500 ctDNA) assesses multiple variant types in 523 cancer-related genes from **cell-free DNA (cfDNA) obtained through liquid biopsies**.

**What is a liquid biopsy, cfDNA, and ctDNA?**\
A liquid biopsy is typically understood as the collection of body fluid, like blood, and subsequent analysis of its cells, proteins, or DNA for disease markers. This is process is less invasive than surgically obtaining tissue samples.

The release of DNA fragments into the blood stream is a naturally occurring process resulting in circulating cell-free DNA (cfDNA). The fraction of circulating cell-free DNA stemming from tumor cells is typically referred to as circulating tumor DNA (ctDNA).

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #2892), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000002892%20-%20Library%20Preparation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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