Liquid Biopsy — Blood Test for Cancer Biomarkers

A liquid biopsy is a laboratory technique that identifies biological markers shed by tumours into the bloodstream or other fluid compartments. As cancerous cells grow, undergo apoptosis, or break down, they release small fragments of genetic material, known as cell-free DNA (cfDNA) or circulating tumour DNA (ctDNA), as well as circulating tumour cells (CTCs) and extracellular vesicles.

By analysing these circulating components with advanced genomic sequencing and digital PCR technologies, clinicians can detect specific genetic alterations, monitor minimal residual disease, and evaluate how a tumour evolves over time. Unlike standard tissue biopsies, which provide a snapshot of a single tumour site, a liquid biopsy can capture genetic material released from multiple lesions throughout the body.

Understanding liquid biopsy matters because cancer constantly evolves during therapy, often acquiring new genetic changes that can cause resistance to treatment. Because drawing blood carries fewer risks and causes less discomfort than repeated surgical biopsies, liquid biopsies can be performed more frequently. This enables your oncology team to monitor your response to therapy in near real-time, pick up subtle signs of disease progression before they appear on radiological scans, and match you to targeted therapies tailored to your tumour's specific mutations. It empowers you and your care team to make timely, highly personalised decisions.

A liquid biopsy typically requires a standard peripheral blood draw into specialised collection tubes designed to preserve fragile circulating cell-free DNA. The plasma is separated in a pathology laboratory and evaluated using next-generation sequencing (NGS) panels or droplet digital polymerase chain reaction (ddPCR). These assays identify somatic single-nucleotide variants, gene fusions, insertions, deletions, and copy number variations shed directly from the tumour.

Liquid biopsies are most established in non-small cell lung cancer, particularly for detecting mutations like EGFR, ALK, and KRAS. They are also widely utilised in colorectal cancer and metastatic breast cancer to identify actionable alterations such as PIK3CA or ESR1 mutations. Increasingly, liquid biopsies are applied in prostate cancer, melanoma, and gastrointestinal tumours to evaluate circulating tumour DNA and monitor treatment effectiveness.

Detecting specific mutations through a liquid biopsy often directly determines drug selection. For example, finding an EGFR T790M resistance mutation in lung cancer points toward third-generation tyrosine kinase inhibitors. In breast cancer, identifying an ESR1 mutation may alter endocrine therapy choices. Liquid biopsies also help track treatment response, allowing clinicians to switch therapies if molecular signs of resistance emerge.