Targeted therapy

Targeted therapy uses drugs to target specific molecules (for example, proteins) inside cancer cells or on their surface. Targeted therapy is also called molecularly targeted therapy. It is used to:

• slow the growth of cancer
• destroy cancer cells
• relieve symptoms caused by cancer

There are different types of targeted therapy drugs. They each work differently depending on what molecule (gene or protein) the drug is targeting. A treatment is chosen based on the types of molecules made by a person’s tumour. Some targeted therapy drugs target specific proteins in cancer cells that aren’t found in normal cells. Other targeted therapy drugs target mutated proteins or mutated genes in cancer cells. This allows doctors to tailor cancer treatment for each person. Targeted therapy is an important part of personalized (precision) medicine, which uses information about a person’s genes and proteins to prevent, diagnose and treat cancer.

Targeted therapy targets the molecules that send signals that tell cancer cells to grow or divide. By targeting these molecules, the drugs block their signals and stop the growth and spread of cancer cells while harming normal cells as little as possible.

Targeted therapy only works if a cancer cell has the gene or protein target that the drug is trying to block. So it isn’t given to everyone. People who are given targeted therapy first have special tests to look for these targets. But even if a person has a certain target, it doesn’t mean that targeted therapy will always work. This is because the protein or gene that the treatment is targeting may be only part of the reason that a tumour is growing. Targeted therapy doesn’t often cure cancer by itself, but it can be very useful when combined with other types of cancer treatment such as surgery, chemotherapy or radiation therapy.

Most targeted therapies are either monoclonal antibodies or small-molecule drugs. Monoclonal antibodies attach to proteins or genes on the surface of cells. They are large and they don’t enter cells easily. Small-molecule drugs describes many of the other types of targeted therapy drugs that are not monoclonal antibodies. These drugs are made up of molecules that are smaller than antibodies. Small-molecule drugs pass through cells easily. They attach to proteins that are inside cells and block their actions. Tyrosine kinase inhibitors and proteasome inhibitors are examples of small-molecule drugs.

Targeted therapy drugs are also grouped by what protein they are targeting or how they work. Some targeted therapy drugs belong to more than one grouping.

Monoclonal antibodies are versions of immune system proteins (which are called antibodies) that are made in the lab. Monoclonal antibodies block a target on the outside of a cancer cell. The target is often another type of protein. They do this by recognizing and locking onto the protein so that it can’t do its job. Monoclonal antibodies can also help chemotherapy and radiation get into cancer cells and destroy them. They do this by locking on to a protein on the cell’s surface, and the chemotherapy or radiation therapy is then taken up (absorbed) by the cancer cell. Monoclonal antibodies are usually given as an injection into a vein (intravenously).

Some types of monoclonal antibodies are also used as immunotherapy since they trigger the immune system to attack and destroy cancer cells. Monoclonal antibodies are easy to recognize because the names always end in “mab.” Monoclonal antibodies that are commonly used to treat cancer include the following drugs.

Trastuzumab (Herceptin) targets tumours that have a lot of HER2 protein (called HER2-positive tumours). Too much HER2 protein is made when there is a mutation in the ERBB2 (HER2) gene, which causes it to make too many copies of itself. Trastuzumab is used to treat HER2-positive cancers including breast, stomach and esophageal cancers.

Bevacizumab (Avastin) attaches to the vascular endothelial growth factor (VEGF) receptor proteins on cancer cells. It is used to treat cancers that make a lot of VEGF receptor proteins including cervical, colorectal and ovarian cancers.

Rituximab (Rituxan) attaches to the CD20 protein on B lymphocytes. It is most often used to treat types of non-Hodgkin lymphoma that have high numbers of abnormal B lymphocytes.

Cetuximab (Erbitux) attaches to the epidermal growth factor receptor (EGFR) proteins on cancer cells. It is used to treat cancers that make a lot of EGFR protein including colorectal cancer and some types of head and neck cancers.

Tyrosine kinases are a part of a protein that acts like a cell’s on and off switch. They are enzymes that play an important role in a cell’s growth and division. Tyrosine kinase inhibitors block these enzymes from sending signals that cause a cancer cell to grow. These drugs are also called signal-transduction inhibitors.

Examples of tyrosine kinase inhibitors include:

Imatinib (Gleevec) targets a tyrosine kinase that causes uncontrolled growth of cancer. Imatinib is most often used to treat some types of leukemia that have the Philadelphia chromosome.

Gefitinib (Iressa) works on cancer cells that have the epidermal growth factor receptor (EGFR) protein. It targets the tyrosine kinase part of the protein. It is sometimes used to treat non–small cell lung cancer but is also being studied in other types of cancer that have a lot of EGFR proteins.

The natural process of a cell dying is a series of programmed events called apoptosis. In some cancer cells, the signals that tell cells to start the process of dying don’t work properly. Apoptosis-inducing drugs help restore the signals that tell cancer cells to die. These drugs interfere with certain proteins or enzymes involved in cell growth and survival. Apoptosis-inducing drugs can also make cancer cells more easily destroyed by chemotherapy.

Examples of apoptosis-inducing drugs include:

Bortezomib (Velcade) is a proteosome inhibitor. It blocks a group of proteins (proteosomes) that cancer cells need to grow. Interfering with proteosomes can help cancer cells die.

Oblimersen (Genasense) is an antisense drug. It blocks the production of BCL2, a protein that promotes cancer cell survival and can cause resistance to anticancer drugs. Blocking BCL2 may make cancer cells more sensitive to anticancer drugs.

Olaparib (Lynparza) is a poly ADP-ribose polymerase (PARP) inhibitor. PARP is an enzyme that helps repair damage to DNA. PARP inhibitors block PARP so cancer cells can’t repair their DNA, which causes them to die.

Angiogenesis is the growth of new blood vessels. A tumour has to make new blood vessels in order to grow, so anti-angiogenesis drugs try to cut off a tumour’s blood supply by stopping it from developing new blood vessels. Examples of angiogenesis inhibitors include:

Bevacizumab (Avastin) attaches to the vascular endothelial growth factor (VEGF) receptor proteins on cancer cells. It blocks VEGF and is used to treat cancers that make a lot of VEGF receptor proteins. Bevacizumab is also a type of monoclonal antibody.

Sunitinib (Sutent) blocks VEGF that triggers blood vessel growth. It also attaches to the VEGF receptor proteins on cancer cells. Sunitinib is also a type of tyrosine kinase inhibitor that prevents the growth of cancer cells.

Thalidomide (Thalomid) interferes with the signals in cancer cells that cause the growth of new blood vessels. It is most often used to treat multiple myeloma.

mTOR inhibitors block the mammalian target of rapamyin (mTOR). mTOR is a protein that controls cell growth and division. In some types of cancer, mTOR doesn’t work properly so cancer cells grow and divide out of control. mTOR inhibitors block the action of mTOR, which can stop the growth of some types of cancer. mTOR inhibitors are used to treat kidney cancer and some neuroendocrine tumours. Examples include temsirolimus (Torisel) and everolimus (Afinitor).

Hormonal therapy drugs are a type of targeted therapy. They work by preventing hormones such as estrogen, progesterone and testosterone from binding to receptors that help cancer cells grow. Find out more about hormonal therapies.

You may have targeted therapy in different ways. For example, it may be given as pills or capsules that are swallowed (orally) or by needle into a vein (intravenously).

Some targeted therapy drugs can only be given in the hospital. You can take others at home. Targeted therapy treatment is based on a set schedule (called a protocol) that is based on your specific condition. Each course of treatment usually involves a treatment period followed by a recovery period.

Targeted therapies may be used alone but are often used with other types of therapy, such as chemotherapy, radiation therapy or both.

Side effects can happen with any type of treatment. Side effects of targeted therapies tend to be mild and go away once the body gets used to the drug. Targeted therapy attacks cancer cells and limits damage to healthy cells, so there are usually fewer and less severe side effects than with chemotherapy or radiation therapy. If certain side effects are severe, your doctor may stop the therapy for a period of time or adjust the dose. Side effects of targeted therapy will depend mainly on the:

• type of drug, combination of drugs or combination of treatment
• dose
• how the drug is given (for example, by mouth or vein)
• your overall health

Targeted therapy side effects may include:

Some types of targeted therapy can cause skin problems during therapy and for some time afterward. The skin can become red, itchy and dry and start to peel or crack. You may also develop a rash or acne. The area around an injection site may become swollen or red. A rash around an injection site sometimes appears shortly after the injection.

Nail changes may also happen with targeted therapy. Skin around the nails can become swollen and red with cracks or open sores.

If you have radiation therapy at the same time as targeted therapy, skin problems tend to be worse.

Your healthcare team may suggest lotions, creams or other medicines that can help relieve skin problems. It is important to protect your skin from the sun during targeted therapy because sun exposure can make skin problems worse.

Find out more about skin problems.

Some targeted therapy drugs can cause high blood pressure (also called hypertension). Blood pressure is tested on a regular basis during treatment. Sometimes the dose of a drug is changed to manage problems with blood pressure or medicine is given to lower blood pressure while taking targeted therapy.

Angiogenesis inhibitors can cause bleeding from the stomach or intestines. Signs of bleeding include throwing up blood or throwing up something that looks like coffee grounds. You may also have blood in the stool.

Angiogenesis inhibitors also carry a risk of developing blood clots. Blood clots are a rare but serious side effect. A blood clot in the leg is called a deep vein thrombosis (DVT). In the most serious cases, a blood clot can break off and travel to the lungs (called a pulmonary embolus, or PE). This can cause shortness of breath, coughing up blood, low oxygen levels in the blood or heart failure in some cases.

Low doses of medicines that thin the blood may be given to help reduce the risk of blood clots. Tell your healthcare team right away if you have any redness, swelling, pain or cramps in the calf of the leg, shortness of breath or if you are coughing up blood or have blood in your stool.

Targeted therapy drugs can slow wound healing and increase the chance of other wound complications, such as infection. Targeted therapy drugs that are linked to poor wound healing, such as angiogenesis inhibitors, are often stopped before a planned surgery.

Be sure to report side effects to the healthcare team. Your team is there to help. Side effects can happen any time during, immediately after or a few days or weeks after targeted therapy. Sometimes late side effects develop months or years later. Most side effects go away on their own or can be treated, but some side effects may last a long time or become permanent.

For information on specific drugs, go to sources of drug information.