Biomarkers and Targeted Therapy: What Your Test Results Mean

Biomarkers are pieces of information found in the tumor or sometimes in the blood that help doctors understand how a cancer behaves. They can be mutations, proteins, gene rearrangements, or other measurable features. The reason this matters is simple: many cancer treatments work best when the tumor has a specific marker. Without that marker, the same treatment may be less useful or not useful at all.

Families sometimes hear the word biomarker and think it is just another technical detail. In modern oncology, it is often much more than that. Biomarker results can influence whether a person gets immunotherapy, targeted therapy, standard chemotherapy first, or a clinical trial recommendation. That is why many oncologists want molecular or biomarker testing completed before treatment begins, especially in cancers where the results change the order of decisions.

Different cancers have different biomarker patterns. In lung cancer, common biomarkers include EGFR, ALK, ROS1, KRAS, MET, and others. In breast cancer, HER2 is especially important, along with hormone receptors such as estrogen and progesterone. In colon cancer, KRAS, NRAS, BRAF, and MSI/MMR can affect treatment choices. MSI/MMR is also important across several cancers because it can suggest whether immunotherapy may work well.

The key idea is not to memorize every biomarker. The key idea is to understand that the tumor may have a specific signature, and that signature can point toward more personalized treatment. If your family hears a list of marker names that feels overwhelming, ask one practical question: “Which of these results would change the treatment plan the most?” That usually brings the conversation back to what matters right now.

PD-L1 is a protein that can help predict whether immunotherapy might be helpful in some cancers, especially certain lung cancers. A higher PD-L1 score does not guarantee a treatment will work, but it can make immunotherapy a more important part of the treatment conversation. Some people hear a high PD-L1 result and assume it means the cancer is worse. That is not what the test is saying. It is telling the team something about how the immune system and tumor may interact.

The exact importance of PD-L1 depends on the cancer type, the stage, and the other biomarker results. It also depends on whether the treatment is being considered alone or in combination with chemotherapy. So PD-L1 is a clue, not a complete answer. A helpful question is: “How does my PD-L1 score affect what you recommend first?”

Targeted therapy is designed to go after a specific molecular abnormality in the cancer. For example, someone with an EGFR mutation in lung cancer may be treated with a drug designed to target that mutation. Immunotherapy works differently. It helps the immune system recognize and attack cancer more effectively. PD-L1 is one example of a marker that can influence immunotherapy decisions.

This difference matters because families sometimes group every “advanced” drug into the same category. They are not the same. A tumor with a strong targetable mutation may push the oncologist toward targeted therapy first. A tumor without that mutation but with a high PD-L1 score may lead to a different plan. This is one reason biomarker testing before treatment is so valuable: it can prevent starting down the wrong road too quickly.

Another point of confusion is the difference between germline and somatic mutations. Germline mutations are inherited and present in all the cells of the body. Somatic mutations happen in the tumor itself and are not necessarily inherited. The same word “mutation” can refer to either one, which is why families often need clarification.

This matters because a somatic tumor mutation may guide cancer treatment, while a germline mutation may also have implications for family members and future screening. If your doctor mentions a mutation, it is reasonable to ask, “Is this a tumor mutation, an inherited mutation, or do we still need genetic counseling to sort that out?” That is not overcomplicating things. It is asking the right question.

If your pathology report does not mention biomarkers, that does not always mean they were forgotten. Sometimes the tests are ordered separately, sometimes they are still pending, and sometimes they are only appropriate in certain cancer types or stages. But if biomarkers are commonly relevant in that disease, it is absolutely worth asking whether they have been ordered and whether treatment decisions should wait for the results.

A good way to phrase it is: “Before treatment starts, are there biomarker or molecular tests we need so we do not miss an option?” That question can be especially important in lung cancer, metastatic disease, rare cancers, or situations where targeted therapy or immunotherapy may significantly change the plan.

• Which biomarkers were tested, and which are still pending?
• Do any of these results open the door to targeted therapy or immunotherapy?
• Should treatment wait until all biomarker results are back?
• Is this mutation inherited or only in the tumor?
• Would these results change clinical trial options?