Precision Oncology: How Biomarkers Guide Cancer Treatment

Precision oncology is an approach to cancer care that uses biomarkers to guide diagnosis, treatment selection, and follow-up. By studying the genetic and molecular features of a tumor, doctors can personalize care and avoid treatments that may be less effective for a particular patient.

Overview

Precision oncology is a modern approach to cancer treatment that looks beyond where a cancer started in the body. It focuses on the biological features of the tumor, including gene changes, proteins, and other molecular signals called biomarkers. These details can help doctors understand how a cancer behaves and which therapies may be most suitable.

Traditional cancer treatment has often been based mainly on the cancer type and stage, such as lung cancer, breast cancer, or colon cancer. Precision oncology adds another layer of information by asking whether the tumor has a targetable mutation, a marker that suggests response to immunotherapy, or a pattern that predicts resistance to certain drugs. This can make treatment decisions more individualized.

Biomarkers do not replace standard cancer care. Instead, they support it. A patient may still need surgery, radiation therapy, chemotherapy, or supportive care, but biomarker information can refine the plan and, in some cases, open the door to targeted treatments or clinical trials that would not otherwise be considered.

What Biomarkers Are and Why They Matter

A biomarker is a measurable feature that gives information about a disease. In cancer care, biomarkers may be found in tumor tissue, blood, bone marrow, or other samples. They can include DNA mutations, gene fusions, extra copies of a gene, protein levels, or patterns of immune activity around the tumor.

Some biomarkers help confirm a diagnosis, while others provide prognostic information, meaning they help estimate how a cancer may behave over time. Many are predictive biomarkers, which means they help show whether a particular treatment is more or less likely to work. This is especially important when deciding between targeted therapy, immunotherapy, chemotherapy, or combinations of treatment.

Common examples include markers such as HER2, EGFR, ALK, BRAF, BRCA1 and BRCA2, PD-L1, MSI-H, and NTRK fusions. Not every marker is relevant to every cancer type. A result is meaningful only when interpreted together with the person’s symptoms, imaging, pathology report, stage of disease, and overall health.

In many cases, biomarker testing can also help avoid unnecessary side effects. If testing suggests that a therapy is unlikely to benefit a tumor, the care team may recommend a different option instead. This is one reason precision oncology is often described as a more tailored or personalized form of cancer treatment.

How Biomarker Testing Is Done

Biomarker testing usually begins with a sample of tumor tissue collected during a biopsy or surgery. A pathologist examines the sample and may order special tests such as immunohistochemistry, fluorescence in situ hybridization, polymerase chain reaction, or next-generation sequencing. These methods look for specific changes in genes or proteins that may guide treatment.

In some situations, doctors may use a blood-based test called a liquid biopsy. This test looks for tiny pieces of tumor DNA circulating in the bloodstream. Liquid biopsy can be useful when a tissue biopsy is difficult, when there is not enough tumor sample available, or when doctors want to monitor how a cancer is changing over time. However, it does not replace tissue testing in every case.

The type of testing depends on the cancer. Some tumors are checked for one or two well-established markers. Others may be assessed with broader molecular profiling that examines many genes at once. Broad testing can be especially helpful in advanced cancers, cancers with limited standard treatment options, or situations where a patient may qualify for a clinical trial.

Test timing also matters. Biomarker testing may be performed at diagnosis, after surgery, when cancer spreads, or if a treatment stops working. Because tumors can evolve, a new biopsy or repeat testing may sometimes provide information that was not present earlier in the disease course.

How Biomarkers Guide Cancer Treatment

One of the main goals of precision oncology is to identify treatments that are more likely to work for a specific tumor. If a cancer carries a targetable alteration, doctors may recommend a medicine designed to block that abnormal pathway. This is the basis of targeted therapy, which can be highly effective in selected patients.

Biomarkers also play an important role in immunotherapy. Markers such as PD-L1 expression, microsatellite instability, or mismatch repair deficiency may suggest that a tumor is more likely to respond to treatments that help the immune system recognize and attack cancer cells. Even when these markers are present, treatment decisions still depend on the cancer type and the patient’s overall clinical picture.

In some cancers, biomarker results influence whether standard treatments should be added, reduced, or changed. For example, biomarker information may support the use of chemotherapy in one setting, while in another setting it may favor a targeted drug or support close monitoring after surgery. Certain markers may also indicate an inherited cancer risk, leading to genetic counseling for the patient and sometimes family members.

Precision oncology can also help when cancer becomes resistant to treatment. A tumor may develop new mutations over time, and repeat testing can sometimes reveal another pathway to target. This can be particularly relevant in advanced disease, where the treatment plan may need to adapt as the cancer changes.

Which Cancers Commonly Use Precision Oncology

Precision oncology is used across many cancer types, although the degree of benefit varies. It is especially well established in some forms of lung cancer, breast cancer, colorectal cancer, melanoma, ovarian cancer, and certain blood cancers. In these diseases, biomarker testing is often a routine part of treatment planning.

For example, some breast cancers are tested for hormone receptors and HER2 status because these markers strongly influence treatment choices. In lung cancer, especially non-small cell types, testing for EGFR, ALK, ROS1, KRAS, BRAF, MET, RET, and other changes may guide therapy. In colorectal cancer, markers such as RAS, BRAF, MSI, and HER2 can shape both targeted and immune-based treatment decisions.

Melanoma may be checked for BRAF mutations, while ovarian and prostate cancers may be evaluated for BRCA-related or other DNA repair pathway changes. In hematologic cancers such as leukemia and lymphoma, molecular testing can help classify the disease and identify therapies directed at specific cellular pathways.

Even when a cancer does not have a clearly actionable biomarker, testing can still be helpful. It may provide prognostic information, help confirm the diagnosis, or identify eligibility for research studies. Precision oncology is therefore useful not only for selecting treatment but also for improving the overall understanding of the disease.

Benefits and Limitations of Precision Oncology

The main benefit of precision oncology is that it can make treatment more individualized. Instead of using a one-size-fits-all approach, doctors can choose therapies based on the tumor’s molecular profile. This may improve the chance of benefit, reduce exposure to less useful treatments, and support more informed discussions about goals of care.

Another advantage is that biomarker testing can sometimes identify options that would otherwise be missed, including targeted drugs, immunotherapies, or clinical trials. For people with advanced cancer, this can expand the range of possible treatments. It may also help explain why a cancer has responded well, poorly, or only temporarily to a previous therapy.

At the same time, precision oncology has important limitations. Not all cancers have a biomarker that changes treatment. Some detected mutations are not actionable, meaning there is no approved therapy linked to them. In other cases, a biomarker may suggest likely benefit, but the treatment may still not work as hoped because tumors are complex and can develop resistance.

Results can also be challenging to interpret. Some findings are well understood, while others are uncertain or of unclear significance. For this reason, biomarker testing is best reviewed by an experienced multidisciplinary team that includes oncologists, pathologists, molecular specialists, and genetic counselors when needed.

What Patients Can Expect During Care

For patients, precision oncology often begins with a conversation about whether biomarker testing is recommended and what questions the test may answer. The care team may explain whether a tissue biopsy is needed, whether previous samples can be used, and how long results may take. Patients may also be asked about family history, prior treatments, and any inherited cancer syndromes in the family.

Once results are available, the oncologist explains what was found and whether it changes the treatment plan. Some people learn that a tumor has a marker linked to a specific drug. Others may hear that no actionable biomarker was found, which can still be useful because it helps narrow the best next steps. If results suggest an inherited mutation, referral for genetic counseling may be advised.

Patients may find it helpful to ask practical questions, such as:

• What biomarkers were tested, and why?
• Do the results affect treatment choices now or later?
• Is more testing needed if the cancer returns or progresses?
• Could the findings have implications for family members?
• Am I eligible for a clinical trial based on these results?

Care is often delivered by a team. This may include medical oncologists, surgeons, radiation oncologists, pathologists, radiologists, genetics experts, and specialist nurses. Near the end of the care pathway, some patients also seek evaluation at centers with advanced molecular diagnostics. Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals diagnose and treat cancer for international patients, including cases where biomarker-guided planning is part of care.

When to Discuss Biomarker Testing With a Doctor

It is reasonable to ask about biomarker testing whenever someone is newly diagnosed with cancer, especially if the cancer is advanced, recurrent, or known to have targetable mutations. Testing may also be appropriate when standard treatments have not worked as expected or when a doctor is considering targeted therapy, immunotherapy, or a clinical trial.

Patients should also discuss testing if there is a strong family history of cancer, cancer at a younger-than-usual age, or multiple related cancers in the same person or family. These situations can sometimes point to an inherited cancer risk that affects both treatment and family counseling.

Medical advice should always be individualized. The right tests depend on the tumor type, the amount of available tissue, prior treatment history, and the patient’s overall condition. A qualified oncology team can explain which biomarkers are relevant and how results may guide the next steps.

Frequently asked questions

What is precision oncology in simple terms?

Precision oncology is a way of treating cancer based on the tumor’s specific biological features, not just its location in the body. Doctors use biomarker testing to look for gene changes or other signals that may help select the most suitable treatment.

Are biomarkers the same as genetic tests?

Not exactly. Some biomarkers involve genetic changes in the tumor, but others measure proteins or immune-related features. Inherited genetic testing is different because it looks for changes a person is born with, while many cancer biomarker tests look at changes that developed in the tumor itself.

Does every person with cancer need biomarker testing?

No. Biomarker testing is very important for some cancers and less useful for others. The need for testing depends on the cancer type, stage, treatment options, and whether the results are likely to change medical decisions.

Can a blood test replace a tissue biopsy?

Sometimes a liquid biopsy can provide helpful information, especially when tissue is hard to obtain or when doctors want to monitor changes over time. However, tissue biopsy is still often needed because it provides more complete diagnostic and molecular information in many cases.

If a biomarker is found, does that guarantee a treatment will work?

No. A biomarker can suggest that a treatment is more likely to help, but it does not guarantee a response. Cancer cells can behave differently from person to person, and some tumors develop resistance over time.

What if no actionable biomarker is found?

This does not mean treatment is not possible. Standard treatments such as surgery, chemotherapy, radiation therapy, or other evidence-based options may still be effective. The result can also help doctors avoid treatments that are less likely to benefit and may guide future testing if the cancer changes.

References

• National Cancer Institute
• American Society of Clinical Oncology
• European Society for Medical Oncology
• World Health Organization
• National Comprehensive Cancer Network

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.