How Does Targeted Therapy Work?
There are different types of targeted therapy, and each works in its own way. For certain cancers, testing can be done to see if any targeted therapies might be available. If so, targeted therapy might be used on its own or along with other types of treatment.
- How do targeted therapies target cancer cells?
- Which biomarkers can be treated with targeted therapy?
- Examples of targeted therapies
- Angiogenesis inhibitors (anti-angiogenesis drugs)
- Kinase inhibitors
- Proteasome inhibitors
- Signal transduction inhibitors
- Other targeted therapies
- Choosing the right targeted therapy
- How does targeted therapy work with other treatments?
- How successful is targeted therapy?
- When treatment plans change
How do targeted therapies target cancer cells?
Targeted therapies are made to find and attack specific areas or substances in or on cancer cells. Or they can detect and block certain kinds of messages sent inside a cancer cell that tell it to grow. A targeted therapy might target:
- Too much of a certain protein on a cancer cell
- A protein on a cancer cell that is not on normal cells
- A protein that is mutated (changed) in some way on a cancer cell
- Gene (DNA) changes that aren't in a normal cell
These gene and protein changes are called biomarkers.
Each targeted therapy has a specific action it takes on cancer cells. Depending on the biomarker it targets, it can:
- Block or turn off chemical signals that tell the cancer cell to grow and divide
- Change proteins within the cancer cells so the cells die
- Stop the formation of new blood vessels that feed the cancer cells
- Trigger your immune system to kill the cancer cells
- Carry toxins to the cancer cells to kill them, but not normal cells
The action a targeted therapy has on cancer cells affects where these medicines work best and what side effects they may cause. Targeted therapies are broadly classified into 2 groups based on the way they work: small-molecule drugs and monoclonal antibodies. Some work in more than one way.
Targeted therapies called small-molecule drugs are lab-made chemicals that are tiny enough to enter a cancer cell once they find it. They work by targeting a specific biomarker or substance inside the cell and blocking it from working. This helps prevent cancer cells from growing and spreading.
The generic names of small-molecule drugs often end in -ib, such as imatinib.
Monoclonal antibodies are proteins made in a lab. They are too big to enter the cancer cell directly. Instead, they aim for and act on the surface of the cell or in the area around the cell to block a specific target. Some monoclonal antibodies work by themselves. Others carry chemotherapy or other treatments to the cancer cells to help destroy them.
The generic names of monoclonal antibodies often end in -mab, such as rituximab.
Most monoclonal antibodies are considered targeted therapy, but some work in a different way, acting on your immune system to help it find and attack cancer cells more effectively. Learn more about monoclonal antibodies that affect the immune system.
Which biomarkers can be treated with targeted therapy?
All cancers start because of gene changes (mutations) that turn normal cells into cancer cells. But cancers can have many different types of mutations or other biomarkers. Even when two people have the same type of cancer (like colon or breast cancer), their cancers may have different biomarkers that affect which treatments might work best.
Some of the more common gene or protein changes in cancer cells that have targeted therapies approved for treatment include:
- ALK genes (some lung cancers or lymphomas)
- BCR-ABL protein (some chronic myeloid leukemias)
- BRAF genes (some colorectal, lung, thyroid cancers, and melanoma)
- BRCA (like BRCA1 and BRCA2) genes (some breast, ovarian, pancreatic and prostate cancers)
- CDK4/6 proteins (some breast cancers)
- C-KIT gene (some leukemias and gastrointestinal stromal tumors)
- EGFR genes (some colorectal and lung cancers)
- HER2/neu (ERBB2) genes (some breast, colorectal, lung, ovarian, pancreatic and stomach cancers)
- KRAS genes (some colorectal, lung and pancreatic cancers)
- MET genes (some lung, thyroid, and renal cell cancers)
- mTOR protein (some kidney cancers)
- NTRK genes (some colorectal, lung, and pancreatic cancers)
- PARP protein (some ovarian cancers)
- PIK3CA genes (some breast, colorectal, lung, and ovarian cancers, or lymphomas and chronic leukemias)
- RET genes (some lung and thyroid cancers)
- ROS1 genes (some lung cancers)
- VEGF genes (some colorectal, hepatocellular, lung, renal cell, and thyroid cancers)
Examples of targeted therapies
In addition to being classified as small-molecule drugs or monoclonal antibodies, targeted therapies can also be grouped based on their specific target or the way that they act against the cancer cell. Some can act in multiple ways and are included in multiple groups. Different types can cause different side effects depending on the specific way they work. Here are some examples:
How they work: To get the blood and nutrients they need to grow, tumors send signals that cause new blood vessels to form nearby. This process is called angiogenesis. Treatment with angiogenesis inhibitors helps stop the formation of new blood vessels by targeting proteins such as vascular endothelial growth factor (VEGF). Blocking this protein can slow or stop cancer growth by limiting its blood supply.
Angiogenesis inhibitors are monoclonal antibodies, so their generic names often end with -mab, such as bevacizumab.
Examples of angiogenesis inhibitors:
- Bevacizumab is used in combination with some types of traditional chemo, immunotherapy, or other targeted therapy. It can be used for some types of cervical, colorectal, liver, non-small cell lung, and ovarian cancers, as well as glioblastoma (a type of brain cancer) and renal cell carcinoma (a type of kidney cancer). Side effects include bleeding, headache, high blood pressure, kidney problems, delayed wound healing, and fatigue.
- Ramucirumab is used in combination with some other targeted therapy or traditional chemo for management of colorectal, liver, non-small cell lung, or stomach cancer. Side effects include bleeding, headache, high blood pressure, kidney problems, delayed wound healing, and fatigue.
How they work: Kinase inhibitors block the action of kinase, a type of protein inside cells that normally helps tumor cells grow. Some of the known kinases that respond to kinase inhibitors include KRAS, EGFR, ALK, PIK3, and BRAF. Blocking these kinases can often stop the growth of the cancer. There are different groups of kinase inhibitors, based on the kinds of proteins they block: tyrosine kinase inhibitors (TKIs), serine/threonine kinase inhibitors, and nonspecific inhibitors.
Kinase inhibitors are small-molecule drugs. Their generic names often end in -nib, such as imatinib.
Examples of kinase inhibitors:
- Osimertinib is a tyrosine kinase inhibitor that targets cancer cells with too much of a protein called epidermal growth factor receptor (EGFR). It blocks EGFR to keep the cancer cells from growing faster. Osimertinib can be used in cancers like non-small cell lung cancer that have certain abnormal EGFR genes. Side effects include low white blood cell count (neutropenia), low platelet count (thrombocytopenia), skin changes (rash), diarrhea, nail changes, cough, and lung problems.
- Imatinib is another type of tyrosine kinase inhibitor that targets cancer cells with the BCR-ABL protein. This protein sends out signals for cells to grow and divide without stopping. Blocking it slows cancer growth. Imatinib can be used for some types of chronic myeloid leukemia or gastrointestinal stromal tumors. Side effects include fatigue, edema, nausea, diarrhea, and muscle cramps.
How they work: Proteasome inhibitors work inside cells by blocking enzyme complexes called proteasomes from breaking down the proteins that keep cell division under control. This disrupts normal cell functions, especially in cancer cells, which produce more abnormal proteins and are more likely to die as a result.
Proteasome inhibitors are small-molecule drugs, with generic names often ending in -mib, such as bortezomib.
Examples of proteasome inhibitors:
- Bortezomib is used to treat multiple myeloma, often in combination with other targeted therapy and steroids. It can also be used to treat some lymphomas, usually after other treatments have been tried. Side effects include skin changes, diarrhea, nausea, low blood counts and nerve damage.
- Carfilzomib is also used to treat multiple myeloma. Like bortezomib, it is used in combination with other targeted therapies. It can also be used to treat Waldenstrom macroglobulinemia (WM). Side effects include high blood pressure, edema, diarrhea, nausea, low red blood counts, fatigue, and headache.
How they work: Signal transduction is the way cells act on signals from hormones and growth factors outside the cell. This process helps normal cells function properly. But cancer cells can alter the signal pathways, allowing them to grow and divide more easily or avoid dying. Signal transduction inhibitors disrupt these abnormal cell signals to help stop the cancer from growing.
Signal transduction inhibitors are small-molecule drugs. Their generic names can have different endings, including -sib and -nib.
Examples of signal transduction inhibitors:
- Idelalisib is a PI3K inhibitor. It targets a protein called phosphatidylinositol 3-kinase that sends signals affecting cell growth. It is used to help treat chronic lymphocytic leukemia after other treatments have been tried. Side effects include skin changes, fever, fatigue, diarrhea, cough, low blood counts, and nausea.
- Dabrafenib is a BRAF inhibitor that acts on changes in the BRAF protein. About half of all melanomas have changes in the BRAF gene, allowing them to make an altered protein that helps them grow. Dabrafenib is often used along with other targeted therapies to treat melanoma that has spread or can’t be removed completely. Side effects include skin changes, fever, fatigue, and nausea.
There are many other types of targeted therapies that work in different ways. Some examples include:
- Antibody-drug conjugates
- Apoptosis inducers
- Gene expression modulators
- Hedgehog inhibitors
- Hormone therapies
- Immunotherapies
- mTOR inhibitors
- PARP inhibitors
- Toxin delivery molecules
Learn about targeted therapy for your cancer type
Choosing the right targeted therapy
Choosing the right targeted therapy is very important. Targeted therapy is sometimes called precision or personalized medicine because even people with the same type of cancer can have different biomarkers. Different targeted therapies are used depending on which biomarkers are found through testing.
Biomarker testing
For certain types of cancers, biomarker testing is done (usually after a biopsy or surgery) to look for biomarkers that could be targeted.
Not all known biomarkers have effective treatments yet, and many are still being studied.
- If a targetable biomarker is found, doctors can match the person with a treatment that is more likely to work.
- If a cancer doesn’t have the biomarker that a targeted therapy is designed to act on, that treatment won’t be effective.
Treatment options
Factors a cancer care team considers when recommending treatment options include:
- The type and subtype of cancer
- The stage of the cancer (where it is, how big it is, and whether it’s spread to other parts of the body)
- Results of biomarker testing
- Your age
- Your overall health and current medications
- Other serious health problems (such as heart, liver, or kidney diseases)
- Goal of treatment
- Types of cancer treatments you have had in the past
The cancer care team also considers the standard-of-care treatment guidelines for specific cancers. They may also offer a clinical trial if one is available and the person is eligible for the trial.
If your treatment plan is not clear, or you are given several possible options, ask your cancer care team about getting a second opinion. It’s important to feel confident that you understand your choices and are making the decision that’s right for you.
How does targeted therapy work with other treatments?
So far, only a few types of cancer are routinely treated using only targeted therapy or a combination of targeted therapies.
More often, targeted therapy is used along with other treatments. Some targeted therapies are even specifically designed to help other treatment work better. For example, they might make cancer cells more sensitive to chemo or block the cancer’s ability to repair damage caused by chemo.
ITargeted therapy may be used:
- To shrink a tumor before surgery or radiation therapy neoadjuvant therapy)
- After surgery or radiation therapy to help kill any remaining cancer cells in the body (adjuvant therapy)
- With other types of medicines, such as traditional chemo, immunotherapy, or hormone therapy
- With other treatments if cancer comes back or doesn't completely go away
How successful is targeted therapy?
Targeted therapy can be very successful at treating cancer. However, there are times it may not work or may stop working. This is usually because:
- The cancer doesn’t have the specific biomarker for the targeted therapy to find and work against. The exact target needs to be present in the cancer cells for a targeted therapy to work. This is why targeted therapies can’t be used for everyone with a certain type of cancer.
- The cancer develops drug resistance. This happens if the cancer cells develop new changes or mutations. If the new change or mutation is not a target for the medicine, the drug will no longer be effective. This is a common reason for targeted therapies to stop working and in many cases, can be tested for by getting another biopsy sample.
- People can respond differently to a targeted therapy. Any variation from person to person affects how well the targeted therapy works against their cancer.
Each person’s cancer is unique, and differences in their genes, type and makeup of cancer, overall health, and how they respond to treatment can all impact the success of targeted therapy. Doctors and scientists are still learning about these drugs and personalized medicine remains a very personal experience.
When treatment plans change
Doctors use guidelines based on research and clinical trials to know the best treatment options. It’s important to get the full prescribed course of targeted therapy to get the most benefit from treatment. But this isn’t always possible.
Sometimes, the treatment plan must be changed. You might develop drug resistance, meaning the targeted therapy stops working. If this happens, your doctor will talk with you about other treatment options.
You may also develop another health problem or serious side effects that require adjusting the dose or schedule to help your body recover. Supportive medicines may also be used to help manage side effects. The goal is to give enough targeted therapy to treat the cancer without causing other serious problems.
In some situations, targeted therapy may be recommended after other types of treatment has been unsuccessful in slowing the growth of the cancer. Learn more about options if cancer treatments stop working or whether a clinical trial may be an option for you.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: June 2, 2025
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