Cancer Biomarker Testing: How It Helps Doctors Choose Treatment

Medically Reviewed By Dr. Sujeet Kumar, DM Clinical Hematology SGPGI Lucknow, EHA Certification in Hematology European Hematology Association, MD SGPGI Lucknow, MBBS NRS Medical College, Kolkata, Senior Consultant - Cancer Care

Updated on: Sep 18, 2026
Published on: Sep 10, 2026

Cancer Biomarker Testing: How It Helps Doctors Choose Treatment

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Introduction

Until recently, most cancer treatment decisions were based on where in the body the cancer started and what the tumour looked like under a microscope. Two patients with the same type of cancer might receive the same chemotherapy regimen, even though their tumours were biologically very different and would respond in entirely different ways.

Biomarker testing has changed this. By examining the biological characteristics of a tumour at the molecular level, oncologists can now identify which specific mutations, proteins or genetic changes are causing an individual patient's cancer and match treatment to the tumour's biology.

What Is Cancer Biomarker Testing?

In cancer, biomarkers are specific molecules, including genes, proteins or other substances, measured in tumour tissue or in the blood. They provide information about the biology of the cancer, how it is likely to behave, and how it is likely to respond to specific treatments.

Cancer biomarker testing (also called molecular profiling or tumour profiling) is the process of analysing a tumour sample or a blood sample to identify the biomarkers present. The results tell the oncologist which gene mutations are driving the cancer's growth, whether the cancer is likely to respond to a targeted therapy or immunotherapy and whether specific drugs are likely to be effective or toxic for this particular patient.

Types of Biomarkers: Genes, Proteins, and Mutations

Cancer biomarkers fall into several main categories.

Gene mutations and somatic alterations: Changes (mutations) in specific genes within tumour cells drive cancer growth. Examples are EGFR mutations in non-small cell lung cancer (NSCLC), BRCA1 and BRCA2 mutations in breast and ovarian cancer, KRAS mutations in colorectal cancer and ALK rearrangements in lung cancer. Each can be targeted by specific drugs that block the abnormal protein the mutated gene produces.
Protein expression: Some biomarkers are abnormal levels of specific proteins that are present on the surface of cancer cells like HER2 overexpression in breast and gastric cancer.
Immune checkpoint markers: PD-L1 (programmed death-ligand 1) expression indicates how likely a tumour is to respond to immune checkpoint inhibitor drugs. PD-L1 testing is now standard before immune checkpoint therapy in lung, bladder, head and neck, and several other cancers.
Microsatellite instability (MSI) and mismatch repair deficiency (dMMR): Tumours that are MSI-high or dMMR have a defect in their DNA repair machinery and are particularly likely to respond to immune checkpoint inhibitors, regardless of where in the body the cancer originated.
Tumour mutational burden (TMB): A measure of the total number of mutations in a tumour's DNA. High TMB is associated with increased response to immunotherapy in some cancer types, as highly mutated tumours are more likely to be recognised and attacked by the immune system.

How Biomarker Testing Is Done: Tissue vs Liquid Biopsy

Biomarker testing can be performed on two main types of sample: tumour tissue and blood.

Tissue biopsy is the standard method for most comprehensive tumour biomarker testing. A tumour sample is obtained surgically or through a needle biopsy and analysed in a molecular pathology laboratory. Comprehensive genomic profiling (CGP) panels analyse hundreds of cancer-relevant genes simultaneously from a single tissue sample. Tissue biopsy provides the most detailed molecular picture but requires an invasive procedure and may not always be feasible.

Liquid biopsy detects circulating tumour DNA (ctDNA) from a simple blood draw. It is particularly useful for monitoring treatment response, detecting resistance mutations when a cancer stops responding to treatment and in situations where tumour tissue is difficult to obtain.

How Biomarkers Help Doctors Choose the Right Treatment

The most direct clinical use of biomarker testing is to identify targetable alterations: specific mutations or protein changes that can be blocked by an existing targeted drug.

Targeted therapy matching: Identifies genetic changes such as EGFR or ALK mutations that can be treated with targeted medicines (EGFR tyrosine kinase inhibitors & ALK inhibitors)
Immunotherapy selection: Testing for PD-L1 expression, MSI status and TMB helps predict which patients are most likely to benefit from immune checkpoint inhibitors.
Avoiding ineffective treatments: Identifying treatments unlikely to work for a specific patient allows those options to be excluded and replaced with more appropriate alternatives, reducing the burden of ineffective treatment, avoiding unnecessary side effects and preserving quality of life.

Biomarker Testing and Access to Clinical Trials

Many clinical trials of new cancer drugs are designed specifically for patients whose tumours carry a particular biomarker. Biomarker testing can therefore open access to experimental treatments that would not otherwise be available.

In India, several ICMR-approved clinical trials and international trials conducted at hospitals require biomarker eligibility testing. A patient whose tumour carries a rare but targetable mutation may be eligible for a trial of a drug not yet widely available. Oncologists with access to comprehensive biomarker profiling are better placed to identify and refer patients to appropriate trials.

Biomarker Testing vs Genetic Testing: What Is the Difference?

These two terms are frequently confused. The distinction is clinically important.

Cancer biomarker testing (somatic testing or tumour molecular profiling) analyses the DNA of the tumour cells themselves. The mutations identified are acquired (somatic) mutations that developed in the cancer cells during a person's lifetime. They are not inherited or passed on to children. The results guide treatment decisions.

Germline genetic testing analyses the DNA in normal cells to look for inherited mutations that a person was born with and may have passed on to their children. BRCA1 and BRCA2 testing for inherited breast and ovarian cancer risk is an example. An oncologist or genetic counsellor can clarify whether a result is somatic or germline.

Cancers Where Biomarker Testing Is Most Useful

Biomarker testing is now standard of care or strongly recommended in the following cancers.

Non-small cell lung cancer (NSCLC): Testing for EGFR, ALK, ROS1, BRAF, MET, RET, NTRK, KRAS G12C, and PD-L1 helps select targeted therapies and immunotherapy
Breast cancer: HER2, ER, PR, BRCA1/2, PIK3CA and PD-L1 testing guides treatment choices
Colorectal cancer: KRAS, NRAS, BRAF, MSI and dMMR testing identifies the most effective treatment options
Any solid tumour (tumour-agnostic testing): MSI-H, dMMR, high TMB and NTRK gene fusions can guide treatment with specific drugs regardless of the cancer's primary site.

Limitations and Things to Consider

Biomarker testing is a powerful tool but has important limitations that patients should understand.

Not every tumour has a targetable biomarker.
Standard tumour profiling can take one to three weeks and for rapidly progressing cancers, treatment may need to begin before results are available.
Comprehensive biomarker profiling is costly and access is concentrated in large urban cancer centres. Many tests are not yet covered under standard health insurance in India, though coverage is expanding under CGHS and some private insurers.

Conclusion: Why Biomarker Testing Matters

Cancer biomarker testing represents one of the most significant advances in oncology of the past two decades. It has transformed the treatment of lung cancer, breast cancer, colorectal cancer and several other common cancers from a one-size-fits-all approach to a precision-guided strategy where treatment is tailored to the specific biology of each patient's tumour.

For patients in India, where the burden of cancer is growing and access to targeted therapies and immunotherapies is expanding, biomarker testing offers a genuine opportunity to receive the right treatment from the start, avoid treatments unlikely to work and access clinical trials that might not otherwise be available. Patients diagnosed with cancer should ask their oncologist whether biomarker testing is appropriate for their diagnosis and what specific tests are recommended before treatment begins.

FAQs

Can cancer biomarker testing tell me which treatment is most likely to work?

Yes, in many cases. If your tumour carries a mutation that is targeted by an approved drug, biomarker testing can identify that match with a high degree of confidence. However not all tumours have targetable biomarkers, and even when a match exists, individual responses to treatment can vary.

Will I need biomarker testing before starting cancer treatment?

Biomarker testing is now standard of care before treatment begins for non-small cell lung cancer, breast cancer, colorectal cancer, gastric cancer and several others. Your oncologist will advise whether and what type of biomarker testing is appropriate for your specific diagnosis and stage.

How long does it take to receive biomarker test results?

Standard protein biomarker tests (such as HER2 or PD-L1 immunohistochemistry) typically return results within one to five working days. Comprehensive genomic profiling using next-generation sequencing, which analyses hundreds of genes simultaneously, typically takes one to three weeks. Liquid biopsy results usually take one to two weeks.

Does every cancer patient need biomarker testing?

Not necessarily. Biomarker testing is most valuable for cancers where targetable mutations are common or where the results directly determine treatment choice. Your oncologist will advise based on your specific diagnosis, stage and treatment options.

Can biomarker testing change my cancer treatment plan?

Yes a biomarker result may switch the planned treatment from standard chemotherapy to a targeted oral therapy, or identify that a planned treatment (such as an anti-EGFR antibody) is unlikely to work because of a specific mutation, prompting a different approach. Biomarker results can also qualify a patient for a clinical trial of a new drug that would otherwise be inaccessible.

Can biomarker testing help predict how my cancer may respond to treatment?

Yes this is one of its primary functions. Predictive biomarkers indicate the likelihood of a response to a specific treatment. Prognostic biomarkers indicate how aggressively the cancer is likely to behave regardless of treatment, helping guide decisions about treatment intensity.

Does health insurance cover biomarker testing?

Coverage varies significantly. In India standard biomarker tests such as HER2, ER, PR and basic mutation testing are increasingly covered by major health insurance policies and under CGHS for government employees. Comprehensive genomic profiling panels remain expensive and are not consistently reimbursed. Patients should check their specific policy and ask the oncology team's billing staff or financial counsellor for assistance in determining coverage before testing begins.

Can biomarker test results change over time?

Yes cancer cells evolve under treatment pressure and new mutations can emerge that confer resistance to a previously effective drug. Repeat biomarker testing (via repeat biopsy or liquid biopsy) at the time of disease progression or treatment failure can identify new resistance mechanisms & guide the selection of the next line of treatment.

What should I ask my doctor before getting biomarker testing?

Useful questions include: Which specific biomarker tests are recommended for my cancer type and why? Will the results change my treatment options? How long will results take and will treatment begin before they are available? If a targetable biomarker is found, which treatment would that lead to? If no targetable biomarker is found, how will that affect my treatment plan?

What happens if my biomarker test does not identify a treatment target?

A result showing no targetable alterations is itself useful information. It confirms that targeted therapies are not appropriate for your tumour, focuses treatment planning on other established options (such as chemotherapy, immunotherapy based on other criteria, or radiotherapy), and may still provide prognostic information about how the cancer is likely to behave.

References

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