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Traditional chemotherapy works by killing cells that multiply quickly, whether normal or cancerous. Targeted therapy, a type of precision medicine, is different. It works by stopping or slowing the growth or spread of cancer.

This happens on a cellular level. Cancer cells rely on certain molecules¡ªoften proteins¡ªto survive, grow and spread. These proteins are usually produced by cancer-causing genes or by the cancer cells themselves.

How does targeted therapy work?

Targeted therapies are designed to interfere with, or target, these molecules or the cancer-causing genes that create them. In some cases, the drug will attach to the molecule it targets, stopping it from doing its job.

In a healthy or cancerous cell, certain molecules need to be in specific locations (like on the cell surface or inside the nucleus) to do their job, for example, sending growth signals or helping the cell divide. Some targeted therapies work by stopping those molecules from reaching those locations. If the molecule can¡¯t get to where it¡¯s needed, it can¡¯t carry out its role in promoting cancer growth.

There are two main types of targeted therapy drugs:

• Small molecule drugs can easily enter the cells and interfere with the molecules inside. They can also be used to interfere with molecules on the surface of the cell.  
• Monoclonal antibodies are larger and work outside of cancer cells. They target molecules on the surface of the cancer cells or nearby. These are made using cloned cells that produce antibodies that interfere with the targeted molecule. Monoclonal antibodies can also be used to deliver a toxic molecule directly into a cancer cell.

What diseases does targeted therapy treat?

Targeted therapy is used to treat certain types of cancer by attacking specific genes, proteins or other factors that help cancer grow. It is commonly used for:

• Breast cancer (HER2-positive breast cancer and triple-negative breast cancer)
• Lung cancer (EGFR, ALK, or ROS1 gene mutations and others)
• Colorectal cancer (KRAS and BRAF gene mutations)
• Melanoma (BRAF mutation)
• Leukemia (Chronic myeloid leukemia, acute lymphocytic leukemia with specific gene changes)
• Lymphoma (certain types with CD markers)
• Kidney cancer
• Thyroid cancer (RET gene mutation)
• Cholangiocarcinoma and bladder cancer (FGFR1-3 gene mutation)

Who gets targeted therapy?

You may be a candidate for targeted therapy if:

• Your cancer has a specific genetic mutation or protein that can be targeted.
• Other treatments like chemotherapy or radiation aren¡¯t effective or cause severe side effects.
• Your cancer has spread (metastasized) and needs a more personalized approach.

Doctors may perform genomic tests to look for abnormalities in tumor DNA or blood. This can determine which genes are mutated or have extra copies and if there are gene abnormalities that can be targeted.

Even if a patient has a molecule that can be targeted, in some cases, the drug stops working after a period of time. This usually occurs when the cancer finds some other way to keep growing despite the treatment. Repeating genomic testing can sometimes help determine how the tumor outsmarted the drug and guide the next steps in treatment.

What happens during a targeted therapy procedure?

Targeted therapy can be given in different ways:

• Pills or capsules: Many targeted therapies come in oral form, taken at home.
• IV infusion: Some drugs are given through a vein at a hospital or clinic.

The steps to receiving targeted therapy are:

1. Testing and treatment plan: Your doctor will run genetic tests to identify if your cancer has a targetable mutation.
2. Starting treatment: You¡¯ll receive your medication as an infusion or pills, usually daily or in cycles.
3. Monitoring and adjustments: Your care team will track your response and adjust your treatment if needed.

Targeted therapies may be given along with other treatments like chemotherapy, radiation or immunotherapy to improve treatment effectiveness.

Targeted therapy side effects

Although targeted therapies are designed to affect cancer cells more than normal cells, they may still have side effects. Side effects depend on the targeted therapy drug a patient is taking.

Common side effects include: 

• Fatigue
• Skin rash or dry skin
• Diarrhea or nausea
• High blood pressure
• Liver problems (elevated liver enzymes)

Less common but serious side effects include: 

• Heart problems
• Lung inflammation
• Blood clotting issues

Your care team will monitor you closely and provide medications or lifestyle adjustments to help manage any side effects.

Learn more about the side effects of targeted therapies.