# What Is a Biomarker? Five cards on the molecular signals that explain why two identical-looking diagnoses behave differently — what a biomarker is, where it is found, and why it changes the treatment plan. ## 1 — Same diagnosis, different story Two patients can share the same lung cancer diagnosis, yet have tumours that act nothing alike — and call for treatments that are just as distinct. The reason comes down to biology. Understanding that biology starts with biomarkers. *Source: American Cancer Society.* ## 2 — What is a biomarker? A **biomarker** is any measurable signal in your body that gives doctors information about your health or disease. Blood pressure is a biomarker. So is a gene mutation. In cancer, biomarkers reveal what is happening at a molecular level — what is driving the tumour, and how it might behave. > The word comes from *biological marker* — a measurable indicator of a biological state or > condition. *Source: National Cancer Institute.* ## 3 — Your tumour has a fingerprint Every tumour has unique biological features — specific genes, proteins, or mutations that act like a molecular fingerprint. That fingerprint is written in the tumour's DNA. Identifying it tells doctors which treatments are most likely to work — and which ones to skip. *Source: NCCN Guidelines.* ## 4 — Tissue or blood Doctors find biomarkers in two main ways: by sampling tumour tissue directly, or by testing blood for tumour DNA that has shed into the bloodstream. > **Liquid biopsy** — testing circulating tumour DNA in blood — is less invasive and makes > repeat testing easier over time. *Source: NCI / FDA.* ## 5 — Matching the right treatment When a biomarker is identified, treatment can be matched to it — like a key designed for a specific lock. This is **precision medicine**: treatment designed for your cancer specifically, not cancer in general. > Not every cancer has a targetable biomarker — but for those that do, this approach can > dramatically improve outcomes. *Source: American Society of Clinical Oncology.* ## Related - [Biomarker Testing](https://nodule.app/biomarker-testing) — the specific driver mutations in lung cancer, NGS panels, and what to ask at diagnosis. - [Terminology library](https://nodule.app/glossary) — definitions for biomarker, NGS, liquid biopsy, and the individual mutations. --- *Educational use only · Not a medical device.* This document mirrors the page at .