Targeted Therapy (Precision Medicine)

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 need specific molecules, often in the form of proteins, to survive, multiply and spread. These molecules are usually made by the genes that cause cancer, as well as the cells themselves.

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. Other times, the drug will physically block the molecule from the place it normally goes. By stopping the normal work of these molecules, cancer’s growth can be slowed or even stopped.

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 finish the job the targeted therapy is made to stop. Repeating genomic testing can sometimes help determine how the tumor outsmarted the drug.

Targeted therapies can be given in pill form or through an infusion and may be given along with another treatment like chemotherapy or immunotherapy.

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 also can be used to deliver a toxic molecule directly into a cancer cell.

Side Effects of Targeted Therapies

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:

• Skin problems, such as rash
• Elevated liver enzymes, which may lead to a change in the drug dosage
• Diarrhea or constipation
• Nausea and vomiting
• Fatigue
• Low red blood cell count, leading to fatigue
• Low white blood cell count, which may increase risk of infection
• Poor blood clotting and wound healing
• High blood pressure