Targeted therapy uses medicines that target certain parts of certain types of cancer cells. They interfere with a cancer cell's ability to grow and survive. The therapies are specific to each person's cancer.

Targeted therapy may be used along with chemotherapy (chemo) for certain types of stomach cancer. It may also be used if other treatments stop working. To be effective, targeted therapy requires that a suitable target be present in your cancer cells. Tests are run on a sample of your biopsy to look for biomarkers. Biomarkers can include genes, proteins, and other factors. For instance, some people have HER2-positive stomach cancer. This means the cancer cells express a protein called human epidermal growth factor receptor 2 protein (HER2). For HER2-positive tumors, a medicine that targets the HER2 receptor protein resulting in decreased cancer cell division might be added to improve success of your chemo.

Most people get targeted therapy as outpatients at hospitals or clinics. You likely won't need to stay overnight. The targeted therapy medicines used to treat stomach cancer are given in a vein through an IV (intravenous) line. They go into your blood and can kill cancer cells all over your body.

• Trastuzumab and fam-trastuzumab deruxtecan-nxki. These medicines are used to treat advanced (later stage) stomach cancers that are HER2-positive.
• Ramucirumab. This medicine may be used to treat any type of stomach cancer if other treatments aren't working. It works by keeping the cancer cells from growing the new blood vessels they need to grow and spread.
• Entrectinib
• Larotrectinib
• Selpercatinib
• Dabrafenib plus Trametinib

Targeted therapy can cause side effects. The side effects depend on the type of medicine you get. They tend to be less severe than side effects from chemotherapy.

Talk with your healthcare providers about what to expect. Side effects tend to occur while you're getting targeted therapy. Once treatment ends, side effects usually slowly go away. Side effects may include:

• Tiredness and weakness
• Fever and chills
• Nausea and vomiting
• High blood pressure
• Headaches
• Cough
• Diarrhea

Rare side effects include:

• Heart damage
• Bleeding
• Blood clots
• Healing problems
• Holes forming in the stomach or intestine, which can lead to infection
• Lung disease

Talk with your healthcare providers about any changes you notice or side effects you have. They may be able to help ease them or keep them from getting worse. Most side effects go away over time after treatment ends.

It's important to know which medicines you're taking. Write down the names of all your medicines. Ask your healthcare team how they work and what side effects they might cause.

Talk with your healthcare providers about what signs to look for and when to call them. Know what number to call with questions or problems. Is there a different number to call when the clinic is closed on evenings, weekends, or holidays?

It may be helpful to keep a diary of your side effects. Write down physical, thinking, and emotional changes. 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 healthcare team to make a plan to manage your side effects.