Targeted therapy is a type of cancer treatment that works by interfering with specific proteins that help tumors grow and spread. Unlike chemotherapy, which kills all rapidly dividing cells in the body (including healthy ones), targeted therapy zeroes in on the molecular changes that make cancer cells different from normal cells. This precision means it can often slow or stop cancer growth while causing less collateral damage to healthy tissue.
How Targeted Therapy Differs From Chemotherapy
Healthy cells in your body only divide when they receive specific chemical signals telling them to do so. Cancer cells bypass this system. Many have changes in the proteins on their surface that tell them to keep dividing whether or not those signals are present. Targeted therapies block or interfere with these proteins, cutting off the instructions that fuel uncontrolled growth.
Some targeted therapies take a different approach entirely: they starve the tumor of its blood supply. Tumors can’t grow beyond a small size without forming new blood vessels, a process called angiogenesis. Certain drugs, known as angiogenesis inhibitors, block the signals tumors send to trigger new blood vessel growth. Without that blood supply, tumors stay small. If a tumor already has blood vessels feeding it, these drugs can cause those vessels to die off, shrinking the tumor.
Chemotherapy, by contrast, attacks any cell that divides quickly. That’s why it causes hair loss, mouth sores, and drops in blood cell counts. Targeted therapy is more selective, though it still has side effects of its own.
The Two Main Types of Targeted Drugs
Targeted therapies fall into two broad categories based on their size and how they reach cancer cells.
Small molecule drugs are tiny synthetic chemicals, small enough to slip through cell membranes and get inside the cell. Once inside, they can block the internal signaling machinery that drives cancer growth. These are typically taken as pills, which makes them convenient for daily use at home.
Monoclonal antibodies are large laboratory-made proteins, roughly 300 times the size of small molecule drugs. Because they’re too big to enter cells, they work on the outside, latching onto proteins on the cell surface or blocking signals floating between cells. These are given through an IV infusion, usually at a clinic or hospital.
The distinction matters practically. If your treatment plan includes a small molecule drug, you’ll likely take a daily tablet. If it involves a monoclonal antibody, you’ll need periodic infusion appointments, though newer formulations of some antibodies now allow injection under the skin.
What Biomarker Testing Means for You
Targeted therapy only works if your cancer has the specific molecular change the drug is designed to block. That’s why doctors order biomarker testing (also called molecular profiling or genomic testing) on a sample of your tumor before recommending targeted therapy. This testing looks for mutations or abnormal proteins that a targeted drug can act on.
In non-small cell lung cancer alone, doctors now routinely test for changes in at least seven different genes: EGFR, ALK, ROS1, BRAF, KRAS, NTRK, and RET. Each of these has an approved drug matched to it. KRAS G12C mutations, for example, account for more than a third of all KRAS mutations in lung cancer patients and have a specific drug designed to block them. RET gene fusions show up in about 1 to 3 percent of lung cancer cases, a small percentage, but for those patients, drugs targeting RET can be highly effective.
This principle extends well beyond lung cancer. HER2 protein overexpression is a well-known target in breast cancer. BRAF V600E mutations guide treatment in melanoma and colorectal cancer. The specific target matters more than where the cancer started. In some cases, the same drug works across multiple cancer types as long as the tumor carries the right molecular change.
Cancers Commonly Treated With Targeted Therapy
The list of cancers with approved targeted options has expanded rapidly. Some of the most established uses include:
- Breast cancer: HER2-positive tumors are treated with drugs that block the HER2 protein, which drives about 20 percent of breast cancers.
- Non-small cell lung cancer: Multiple targeted drugs exist for EGFR, ALK, ROS1, BRAF, KRAS G12C, NTRK, and RET mutations.
- Colorectal cancer: Tumors with BRAF V600E mutations can be treated with drugs that block the BRAF protein, often combined with other agents.
- Melanoma: BRAF mutations are found in roughly half of melanomas, making BRAF-targeting drugs a standard option.
- Chronic lymphocytic leukemia: Drugs that block specific enzymes driving the growth of these blood cancer cells.
- Multiple myeloma: Newer targeted approaches include bispecific antibodies that help the immune system recognize and attack myeloma cells.
New approvals continue at a steady pace. In early 2026 alone, the FDA approved targeted options for HER2-mutant lung cancer, BRAF-mutant colorectal cancer, chronic lymphocytic leukemia, multiple myeloma, and platinum-resistant ovarian cancer, among others. The field is expanding into tumor types that previously had limited options.
Common Side Effects
Targeted therapy is easier on the body than chemotherapy in many ways, but it isn’t side-effect free. Because the proteins these drugs target sometimes play roles in healthy tissues too, you can experience effects that reflect which protein is being blocked.
The most common side effects include skin problems (rash, itching, or dry skin), diarrhea, high blood pressure, and potential damage to the thyroid, liver, or kidneys. Skin reactions are especially common with drugs that block growth factor receptors, sometimes showing up as an acne-like rash on the face and upper body within the first few weeks of treatment. High blood pressure tends to occur with angiogenesis inhibitors, since the same blood vessel signals they block in tumors also play a role in normal blood pressure regulation.
Most of these side effects are manageable. Your care team will monitor blood pressure, organ function, and blood work at regular intervals throughout treatment. Skin reactions often improve with moisturizers and topical treatments. Diarrhea can usually be controlled with medication adjustments. The key difference from chemotherapy is that severe drops in blood cell counts, significant hair loss, and intense nausea are far less common.
How Long Treatment Lasts
Unlike chemotherapy, which is typically given in defined cycles with a planned end date, targeted therapy often continues for as long as it’s working and you’re tolerating it. For some people, that means months. For others, it means years. Small molecule drugs taken as daily pills can become a long-term part of your routine, similar to taking a blood pressure medication.
One challenge with targeted therapy is that cancers can develop resistance over time. The tumor acquires new mutations that allow it to grow despite the drug. When that happens, doctors may switch to a different targeted drug that works through a slightly different mechanism, or combine targeted therapy with other treatments. In some cancers, second and third-generation drugs have been developed specifically to overcome common resistance mutations, giving patients additional options when the first drug stops working.
What to Expect Getting Started
If your oncologist recommends targeted therapy, the process typically begins with biomarker testing on your tumor tissue. Results can take one to three weeks depending on how many genes are being tested. Once a targetable mutation is identified, your doctor will match it to the appropriate drug.
For oral medications, you’ll pick up your prescription from a specialty pharmacy and take it at home, usually once or twice daily. You’ll have regular check-in appointments to monitor side effects and check whether the treatment is controlling the cancer, typically through imaging scans every two to three months. For IV-based therapies, you’ll go to an infusion center on a set schedule, often every two to three weeks.
Not every cancer has a targetable mutation. If biomarker testing doesn’t reveal a match, your oncologist will discuss other treatment approaches like chemotherapy, immunotherapy, or a combination. The availability of targeted therapy depends entirely on what’s driving your specific tumor at the molecular level.