What Is Targeted Therapy?

Targeted therapy uses drugs or other substances to block or interfere with molecules that cancer cells rely on. These targets may include abnormal proteins, mutated genes, or signaling pathways that tell cancer cells to keep growing. Rather than broadly attacking all rapidly dividing cells, targeted therapy is meant to focus on a particular vulnerability in the tumor.

A simple way to think about it is this: if cancer cells are being driven by a specific “switch,” targeted therapy aims to turn that switch off. In some cases, the treatment blocks growth signals. In others, it cuts off the tumor’s blood supply, triggers cancer cell death, or helps the immune system recognize the cancer more effectively.

How Does Targeted Therapy Actually Work?

Targeted therapy works by interfering with the biological processes cancer cells depend on. According to NCI, these treatments can block or turn off chemical signals that tell cancer cells to grow, prevent tumors from making new blood vessels, help kill cancer cells, or deliver cell-killing substances directly to cancer cells. The exact mechanism depends on the drug and the target involved.

Some targeted therapies work outside the cancer cell by attaching to a marker on its surface. Others work inside the cell by blocking internal signals that control survival or division. The American Cancer Society explains that this is why targeted therapies are often divided into monoclonal antibodies and small-molecule drugs. Monoclonal antibodies are larger and usually act on targets found on the outside of cells, while small-molecule drugs are small enough to enter cells and affect targets inside them.

Why Is Targeted Therapy Different from Chemotherapy?

The biggest difference is specificity. Chemotherapy generally attacks cells that divide quickly, which includes cancer cells but also some healthy cells such as those in the hair follicles, digestive tract, and bone marrow. Targeted therapy is designed to act more selectively on cancer-related changes, which may spare more normal tissue. The American Cancer Society notes that targeted therapy acts on specific cancer cells, while traditional chemotherapy is cytotoxic to many cells, including healthy ones.

That does not mean targeted therapy has no side effects. It still can, and sometimes the side effects can be serious. But the pattern of side effects is often different because the treatment is aimed at a more specific pathway or protein.

Who Can Receive Targeted Therapy?

Not every patient is a candidate for targeted therapy. These treatments are usually most useful when a tumor has a biomarker or molecular feature that the drug is designed to target. That is why doctors often recommend biomarker testing, also called tumor profiling or molecular testing, before choosing treatment. NCI explains that biomarker testing finds changes in your cancer that could help your doctor choose a treatment.

This is a key part of precision medicine. Two patients may both have lung cancer, breast cancer, or colorectal cancer, but only one may have a targetable mutation or protein that makes targeted therapy a good option. In that sense, the question is not just what type of cancer a person has, but what is driving that cancer at the molecular level.

Where Does Liquid Biopsy Fit In?

In some situations, doctors may use a liquid biopsy to help guide targeted therapy. These tests use a blood sample to look for tumor DNA shed into the bloodstream. NCI has reported that FDA-approved liquid biopsy tests can identify genetic changes in tumor DNA from blood and help doctors choose a targeted therapy or immunotherapy that is more likely to work.

Liquid biopsy is especially useful because cancer can change over time. NCI has also noted that tumor markers used to decide whether someone is a candidate for targeted therapy can sometimes be measured through liquid biopsy, and that blood-based testing may help doctors track resistance or monitor how treatment is working. However, liquid biopsy does not replace every tissue biopsy, and its usefulness depends on the cancer type and clinical setting.