Biomarker Testing — Uncovering the Molecular Profile of Cancer

Biomarker testing refers to laboratory analyses designed to identify specific genetic alterations, protein expressions, or epigenetic modifications characteristic of a patient's malignancy. Also known as molecular profiling, genomic testing, or tumour profiling, it moves diagnostic oncology beyond simple microscopic staging and organ-of-origin definitions into functional molecular subtyping.

Techniques including next-generation sequencing (NGS), polymerase chain reaction (PCR), immunohistochemistry (IHC), and fluorescence in situ hybridisation (FISH) identify actionable abnormalities. These include mutations, gene fusions, copy number variations, and overexpression of surface proteins that drive oncogenesis or predict therapeutic vulnerability.

Biomarker testing is the foundation of precision oncology. It guides the selection of targeted therapies and immunotherapies matched directly to the tumour's vulnerabilities. Furthermore, biomarker results help predict prognosis, assess recurrence risks, and uncover eligibility for clinical trials. Without testing, critical treatment options may be overlooked, leaving patients with less effective or overly toxic general regimens.

Tests are performed on formalin-fixed paraffin-embedded tissue obtained from surgical biopsies, or via liquid biopsy analysing cell-free circulating tumour DNA (ctDNA) in peripheral blood. Common assays include multigene next-generation sequencing panels, immunohistochemical staining, and droplet digital PCR to quantify minimal residual disease or detect emergent resistance mutations.

Biomarker testing is standard practice in non-small cell lung cancer (assessing EGFR, ALK, ROS1, KRAS, BRAF), colorectal cancer (KRAS, NRAS, BRAF, MSI/MMR), breast cancer (ER, PR, HER2, BRCA), and melanoma (BRAF V600). It is also utilised across thyroid, ovarian, prostate, and gastrointestinal stromal tumours.

Identifying a positive biomarker directly informs drug therapy: for instance, detecting an EGFR mutation prompts the use of tyrosine kinase inhibitors, while high PD-L1 expression supports checkpoint inhibitor immunotherapy. Conversely, testing can prevent futile treatment, such as identifying KRAS mutations that predict resistance to anti-EGFR therapies in metastatic colorectal cancer.