Targeted therapy medicines attack certain proteins or cell functions that help cancer cells grow. Like chemotherapy, these medicines go all through the body, but they work in different ways. This means they can sometimes help even if chemotherapy isn't working. These medicines mainly target cancer cells. So the side effects are often different and sometimes less severe than chemotherapy side effects.

Not everyone with colorectal cancer will need targeted therapy. Deciding if targeted therapy is a choice for you will depend mainly on these factors:

• The stage of your cancer
• Details about your cancer cells, such as specific proteins found on the surface of the cancer cells or certain gene changes in the cells. Cancer cells are tested for these proteins and gene changes in a lab.
• Your age and overall health
• Your concerns about side effects
• What treatments you may have had before

Targeted medicines are used to treat some colorectal cancers that have spread to other parts of the body. Some of these medicines are also being studied to see if they might help if given after surgery for less advanced cancers.

These medicines are most often given along with chemotherapy. But some may also be used alone if chemotherapy is no longer working.

Several types of targeted medicines are now used for colorectal cancer.

Tumors need new blood vessels to grow beyond a certain size. Some targeted medicines work by blocking new blood vessels from forming. These include:

• Bevacizumab.
• Ramucirumab.
• Ziv-aflibercept.
• Fruquintinib.

Epidermal growth factor receptor or EGFR is a protein that's often found in high levels on cancer cells and helps them grow. Some targeted medicines work by attacking the EGFR protein. These include:

• Cetuximab.
• Panitumumab.

These medicines don't work in people whose cancer cells have certain gene mutations. Your doctor will test a sample of your tumor for these mutations before you get one of these medicines.

Regorafenib is a type of targeted medicine known as a multikinase inhibitor. It blocks several different proteins (kinases) in cancer cells that normally help them grow.

Encorafenib is another targeted therapy medicine that can shrink tumors or slow cancer growth. It works by attacking BRAF protein that helps cancer cells grow.

Trastuzumab combined with pertuzumab, tucatinib, or lapatinib target a protein called HER2. It may help when there is too much of this growth-promoting protein on cancer cells.

Larotrectinib, entrectinib, and repotrectinib target a specific NTRK gene change found in some colorectal cancer cells. They might be used if other treatments aren't working anymore.

Before treatment starts, you'll meet with a medical oncologist. This is a doctor who specializes in treating cancer with medicines. They will discuss your treatment choices with you and explain what you might expect.

How you get targeted therapy depends on which medicines are used. Some are pills that you take at home. Others go right into your blood through an I.V. (intravenous) line in a vein. This may take several minutes or hours.

In most cases, you will have targeted therapy as an outpatient. This means that you get it at a hospital clinic, infusion center, or your doctor's office, and you go home the same day. Rarely, you may need to stay in the hospital during treatment.

You'll be watched for reactions during your treatments.

Some targeted medicines are given along with chemotherapy. Others are given alone.

Side effects of targeted therapy are different for everyone. They also depend on which medicine you get. Ask your doctor about possible side effects you should watch for. Tell your doctor about any changes or side effects you notice. There may be ways to help you feel better and keep side effects from getting worse. In most cases, side effects will get better over time after treatment ends.

These are some of the possible side effects of targeted therapy:

• Allergic reactions, often during the infusion. If you have a reaction, it will likely be short-term and treatable. If this happens, your doctor will talk with you about whether you can keep taking this type of medicine.
• Acne-like skin changes on your face and chest. Treatment can't prevent these skin changes. But there are ways to make them less of a problem and keep them from getting infected.
• High blood pressure
• Headaches
• Fever
• Higher risk for infection because of a low white blood cell count
• Feeling very tired during treatment and for a while after
• Loss of appetite
• Belly (abdominal) pain
• Sores in the mouth and throat
• Weight loss
• Diarrhea
• Joint pain

Rare but more severe side effects are:

• Blood clots and an increased risk for heart attack and stroke. Your doctor will watch you for this side effect. Let them know right away if you have chest pain, shortness of breath, or numbness or weakness, or if you feel dizzy or faint.
• A GI perforation. This is an opening in the stomach or intestine. Tell your health care team right away if you have any new pain, constipation, or vomiting.
• Bleeding inside the body (internal bleeding). Symptoms include coughing up blood, having blood in your stools or urine, or bleeding from your nose or gums.
• Protein in the urine. This is a sign of kidney damage. Your doctor will check a urine sample before and during your treatment to see if there is too much protein in it.
• Hand-foot syndrome. Symptoms include redness, irritation, or pain in your hands and feet.
• Liver damage. Symptoms include yellowing of your skin or the whites of your eyes.
• Slow wound healing. Let your doctor know if you have any wounds that aren't healing well.
• Heart damage. Your heart function will be checked before and during your treatment. Let your doctor know if you have shortness of breath, leg swelling, or a fast heartbeat.

It's important to know which medicines you're taking. Write down the names of your medicines. Ask your health care team how they work, how to take them, and what side effects they might have.

Talk with your health care providers about what signs to look for and when to call them. Know what number to call with problems or questions. Is there a different number to call after office hours or on holidays and weekends?

It may be helpful to keep a diary of your side effects. A written list will make it easier for you to remember your questions when you go to your appointments. It will also make it easier for you to work with your health care team to make a plan to manage your side effects.