Early diagnosis and prediction of therapeutic responses are crucial in cancer patients to tailor and optimize the treatment, increase the likelihood of cure, reduce side-effects, and avoid overtreatment.

Liquid biopsy allows the analysis of tumors using biomarkers circulating in fluids such as the blood.
Blood contains two types of cancer-derived materials that are susceptible to detailed molecular analysis: intact circulating tumor cells (CTCs) and cell-free circulating tumor DNA (cfDNA; also referred to as circulating tumor DNA, or ctDNA). As tumors increase in volume, the capacity of phagocytes to eliminate and clear apoptotic and necrotic fragments can be exceeded, leading to passive release of cfDNA into the bloodstream. Physicians can use the blood drawn from a patient's arm to analyze DNA that tumors typically shed into the bloodstream. Depending on the tumor size and vascularity, the amount of cfDNA released in the circulation can vary from 0.01% to 90% of all DNA present in plasma. Therefore, liquid biopsies provide a noninvasive approach to tumor molecular profiling without having to obtain tumor tissue.


Cancer biomarkers are used in three primary ways:

Diagnostic

To diagnose conditions, as in the case of identifying early stage cancers.

Prognostics

To forecast how aggressive a condition is, as in the case of determining a patient's ability to fare in the absence of treatment.

Predictive

To predict how well a patient will respond to treatment.

The measurement of genomics, transcriptomics, epigenomics, proteomics, metabolomics and other ‘omics’ methods can be used for cancer diagnosis, prognosis, and epidemiology, the cancer biomarker can be classified by the ‘omics’ type.