by Jason Wasserman MD PhD FRCPC
April 17, 2026
A biomarker is a measurable feature of a cancer — a specific protein, gene change, or other detectable characteristic — that tells doctors something useful about the cancer and how to treat it. Biomarker testing has become one of the most important parts of modern cancer care. Rather than treating all cancers of the same organ the same way, doctors now use biomarker results to tailor treatment to the individual characteristics of each person’s tumour.
What do biomarkers tell doctors?
Different biomarkers serve different purposes, and many serve more than one at the same time:
- Confirming the type of cancer. Some biomarkers help identify exactly what type of cancer is present — especially when cancers from different origins look similar under the microscope.
- Predicting how the cancer will behave. Some biomarkers indicate whether a cancer is likely to grow quickly or slowly and whether it is likely to come back after treatment. These are called prognostic biomarkers.
- Guiding treatment decisions. This is the most important role biomarkers play today. Some biomarkers predict whether a specific drug is likely to work — or not work — for a particular cancer. These are called predictive biomarkers. For example, a KRAS mutation in colorectal cancer predicts that certain drugs will not be effective, whereas HER2 overexpression in breast cancer predicts that HER2-targeted drugs will be effective. These results directly determine which treatments are offered.
- Identifying inherited cancer risk. Some biomarkers — such as mutations in BRCA1 or BRCA2 — indicate an inherited change that increases the risk of cancer in the patient and their family members.
- Monitoring for recurrence. After treatment, certain biomarkers can be measured in the blood over time to monitor for signs that cancer is returning.
How are biomarkers tested?
Biomarker testing is usually performed on tumour tissue collected during a biopsy or surgery. The most common laboratory methods are:
- Immunohistochemistry (IHC) — detects specific proteins in tumour tissue using color-producing antibodies.
- Fluorescence in situ hybridization (FISH) — detects gene amplifications, deletions, or rearrangements at the DNA level.
- Next-generation sequencing (NGS) analyzes many genes simultaneously to identify mutations and other genetic changes in a single test.
- PCR (polymerase chain reaction) — amplifies and detects specific known mutations with high sensitivity.
Will my pathology report include biomarker results?
Not every report includes biomarker testing. Whether testing is performed depends on the type of cancer, its stage, and the information needed to guide treatment. For many cancers — especially those that are more advanced or where targeted treatments exist — biomarker testing is now a standard part of the initial workup. For other cancers, particularly those treated with surgery alone at an early stage, it may not be necessary. Your oncologist or pathologist can explain which biomarkers were tested and what the results mean for your specific situation.
For a detailed explanation of biomarker categories, how results are reported, and what specific results mean for different cancer types, see the full guide: What is a Biomarker? — Biomarker Guide.
Questions to ask your doctor
- Was biomarker testing performed on my tumour, and what were the results?
- Do my biomarker results affect which treatments I am eligible for?
- Do any of my results suggest an inherited condition that may affect my family?
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