Traditional chemotherapy works by killing cells that multiply quickly, whether normal or cancerous. Targeted therapy, also called 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.
Because targeted therapies are made to work on specific molecules, doctors usually perform blood or DNA tests to see if and how many of these molecules are present in the patient’s body. If there are not enough, the drug will not be given. Even if a patient has enough of the targeted molecule, 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.
Targeted therapies can be given in pill form or through an infusion and are often given along with another treatment like chemotherapy or radiation. There are two main types of targeted therapies drugs:
- Small molecule drugs target molecules that are inside cancer cells themselves. Because of their small size, they can easily enter the cells and interfere with the molecules inside.
- 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
While targeted therapies generally have fewer side effects than chemotherapy, they can still be serious. Side effects depend on the targeted therapy drug a patient is taking. Common side effects include:
- Skin problems, including hives and intense itching
- Allergic-like reactions, including trouble breathing, tightness in the chest or throat, dizziness and swelling in the lips or tongue
- Elevated liver enzymes
- Diarrhea or constipation
- Nausea and vomiting
- Low blood cell counts
- Poor blood clotting and wound healing
- High blood pressure
Each cancer patient is unique. And when developing a cancer treatment plan, our doctors consider all of the things that make patients unique, including diagnosis, medical history and treatment preferences. Targeted therapy enables us to personalize cancer treatment even further by tailoring drugs to the genetic characteristics of a patient’s specific tumor.
“Targeted therapy attacks the genetic change within the cancer cell regardless of the tumor type, so we don’t worry if it’s breast cancer, lung cancer or prostate cancer,” says Vivek Subbiah, M.D., clinical medical director of MD Anderson’s Clinical Center for Targeted Therapy. “We focus on the DNA of the cancer cells.”
Sometimes referred to as precision medicine or as personalized medicine, targeted therapy aims to stop or slow the growth of cancer. Targeted therapy drugs are given either as a pill or through an IV.
How targeted therapy personalizes cancer treatment
Cancer develops when a normal cell’s genes change, causing the cell to quickly divide and multiply out of control. The change in the cell’s genes is called a mutation. About 5-10% of cancers are caused by genetic mutations passed from parent to child (such as BRCA1 and BRCA2), but many are caused by factors such as age, sun damage or tobacco use. No matter how the mutation forms, targeted therapy works the same.
Targeted therapy is different than traditional chemotherapy. While chemotherapy kills all cells that multiply quickly regardless of whether they’re cancerous, targeted therapies are designed to find and slow the growth of the cells that have a particular mutation. The mutation is identified in a process called next-generation sequencing. During this process, a small tissue sample from the tumor is removed and tested.
Targeted therapy side effects
Because targeted therapies attack cancer cells, some patients experience fewer side effects than with chemotherapy. Although it depends on the type of targeted therapy you receive, possible side effects can include diarrhea, skin changes, such as itchiness, rash and changes in skin pigmentation, and problems with bleeding, blood clotting and high blood pressure.
Phase I clinical trials focus on making targeted therapy available for more patients
Targeted therapy may not be an option for everyone. Not every patient’s tumor carries a genetic mutation that’s been identified as cancer-causing or that has a potential treatment option. And just like chemotherapy, it’s not guaranteed to work in all patients.
Currently, targeted therapies approved by the U.S. Food and Drug Association (FDA) are available for patients with BRCA, BRAF, EGFR, ALK, ROS1 and HER2 genetic mutations. These mutations have been linked to breast cancer, colorectal cancer, lung cancer and melanoma, among several others.
But researchers are constantly working to identify more cancer-causing genes and, in turn, develop new targeted therapies through Phase I clinical trials. The goal is to build on the successes of existing targeted therapies by combining them with other targeted therapies, as well as other treatments like chemotherapy, immunotherapy and radiation therapy.
“We want to know if a drug works in treating these cancers, but we also want to know about the drugs that don’t and we want to know why not,” Subbiah says.
Phase I targeted therapy clinical trials offer more time
With some widely-used FDA-approved cancer drugs, only 2% to 20% of patients see a response. “Sometimes, these drugs are only adding days to a patient’s life,” Subbiah says. But in some early-phase clinical trials testing new, experimental targeted therapy drugs, Subbiah and his team have seen 35% to 77% of patients respond well.
“These mutations can be rare, like picking a needle out of a haystack. But there is a theme here -- the response rates are higher when we match right therapies to the right genetic makeup,” Subbiah says. “So I encourage patients to keep an open mind, ask for genetic testing of the tumors and talk to their doctor about the possibility of joining a Phase I clinical trial.”
Historic advances and what’s on the horizon for targeted therapy
MD Anderson’s clinical trials have led to FDA approval of targeted therapies for several rare diseases, including the first ever FDA-approved treatment for BRAF V600E mutation-positive anaplastic thyroid cancer and BRAF V600E mutation-positive Erdheim-Chester disease. In addition, research led by David Hong, M.D., found the drug larotrectinib effectively treats 17 cancer types that have the TRK gene mutation.
“Right now, we’re excited about RET inhibitors,” Subbiah says. RET-driven cancers include medullary and papillary thyroid cancers, non-small cell lung cancer, colorectal cancer and bile duct cancer, all of which have historically been difficult to treat.
“We’re finding more genetic mutations each day, and clinical trials are helping us find new therapies that will benefit even more patients,” Subbiah says. “If targeted therapy isn’t an option for you today, that doesn’t mean there won’t be one for you in the near future. In the last five years, I’ve seen amazing drugs come into the clinic for our patients.”
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