As cancer research continues to learn more about how gene changes in cells can cause cancer, this research is helping to introduce new types of cancer drugs. One form of cancer treatment that involves the use of these drugs is referred to as targeted therapy.
Until fairly recently, only a few types of cancers could be treated with targeted therapy, but now these drugs are used to treat many different types of cancer, such as breast cancer, colorectal cancer, lung cancer, pancreatic, lymphoma, leukemia and melanoma.
While targeted therapy drugs used in cancer treatment are generally considered as chemotherapy, these drugs do not work the same as standard chemotherapy drugs, which often attack a patient’s healthy cells along with the cancer cells.
Currently there are a number of targeted therapies now approved by the FDA to treat many types of cancers. In addition, clinical trials are continuing to look for additional drugs aimed at new targets that have recently been discovered.
How Does Targeted Therapy Work?
The basis of targeted therapy in cancer treatment is that it “targets” cancer cells. Targeted therapies work by going straight to the genes and proteins in cancer cells to halt their ability to grow and spread.
Every human cell contains nearly 30,000 genes. And each of these genes produces a different protein, which also performs a different task for the cell. The job of targeted therapies is to stop specific proteins from helping cancer survive. When certain proteins are blocked, or stop working altogether, the cancer cells stop growing and die.
Matching a Patient to a Treatment
Recent studies show that not all tumors have the same targets, which explains why a targeted therapy treatment may not work for every patient. A patient’s tumor tissue must be first tested to determine if they have an appropriate target.
For instance, some patients may have an appropriate target for a particular targeted therapy, allowing them to be treated with that therapy. For other types of cancer, a patient may not have an appropriate target. The use of a targeted therapy may be restricted to patients whose tumor has a specific gene mutation that codes for the target, where as patients who do not have this mutation would not be good candidates, as the therapy would have nothing to target.
In some instances, patients may be candidates for targeted therapy if they meet specific criteria, such as their cancer did not respond to other types of therapies, the cancer has spread, or if the cancer is inoperable. The criteria is set by the FDA when it approves specific targeted therapies.
Examples of Targeted Therapies
While it is currently an exciting time for cancer research in regards to targeted therapy, as more are being approved to treat different types of cancer, these targeted therapies will still not benefit patients whose tumor does not contain a proper target. And in some instances, even if there is a proper target, this still does not guarantee that the treatment will work. Patients are encouraged to follow up with their health care team to gain more information about possible therapies and treatment options.
Here are a few examples of targeted therapies used for different types of cancer:
Research shows that roughly 20% to 25% of all breast cancers have too much of a protein called human epidermal growth factor receptor 2 (HER2). This protein is responsible for stimulating tumor cell growth. If a patient’s test results show the cancer is HER2 positive, there are several FDA approved drugs that may be recommended as as targeted therapy options. For example Herceptin (trastuzumab) was developed to target cancers that over produce the HER2 protein. Kadcyla, or T-DM1, is yet another targeted drug therapy for treating women with stage 2 or stage 4 metastatic breast cancer that is also HER2-positive. Other targeted therapies are being evaluated in clinical trials to see how well they work in treating breast cancer. Most new targeted therapies are given first to women with metastatic breast cancer. As more targets are identified and new therapies are developed, patients will be eligible for treatments that work best for their type of breast cancer.
More cancer research is confirming that drugs which block the epidermal growth factor receptor (EGFR), often overproduced in this type of cancer, may be effective for stopping or slowing the growth of colon or rectal cancer. Erbitux is an example of a targeted therapy used for metastatic colorectal cancer.
Cancer drugs that block the epidermal growth factor receptor (EGFR) may also be effective in stopping or slowing the growth of certain types of lung cancer, especially if the EGFR gene contains certain mutations. Gilotrif (Afatinib) is a recent FDA approved targeted therapy for the treatment of non-small cell lung cancer.
Lynparza (olaparib) is recently FDA approved targeted therapy for various types of advanced ovarian cancer that are related to defective BRCA genes. This particular type of drug is considered a PARP inhibitor.
About 50% of diagnosed melanomas have a mutated gene referred to as the BRAF gene. Current research confirms that specific BRAF mutations provide good drug targets. While the FDA has approved several BRAF inhibitors, these drugs should not be used by patients whose tumors do not have these mutations. Zelboraf (Vemurafenib) is an example of targeted drug therapy used for metastatic melanoma.
Currently there are a number of clinical trials underway on many different types of cancer to investigate new targets and drugs aimed at them.
Side Effects with Targeted Cancer Therapies
Even though targeted therapy does not generally attack a patient’s healthy cells the way standard chemo drugs may, a patient may still experience some side effects with this treatment. These side effects will largely depend on what the drug targets. For instance, some drugs will target substances that are more common on cancer cells, but may also be found on healthy cells. When the drug from therapy treatment attacks more than one target, side effects are more likely to occur.
Common Side Effects
Skin Problems Many targeted therapy drugs can cause a rash or other types of skin changes. In fact, more than half of patients taking a certain targeted therapy drug have experienced some type of skin related side effect. These problems usually develop slowly over days to weeks and are not signs of a drug allergy. However, allergic reactions to these drugs generally start suddenly, usually within minutes to hours from when the drug was given. These side effects may include hives and intense itching. Other allergic reactions may include serious side effects like difficulty breathing, a tightness in the throat, dizziness, or swelling of the tongue or lips.
High Blood Pressure Some targeted therapies may cause a patient’s blood pressure to rise. Unfortunately, there is not much that can be done to prevent this, but your health team will routinely monitor blood pressure closely for patients taking a drug with this type of side effect. Some patients may require medicine to help bring their blood pressure back down to a safe level while they are using a targeted therapy.
Blood Clotting Other targeted cancer drugs may interfere with the formation of new blood vessels. This may lead to a patient experiencing problems with bruising and bleeding. These drugs may also cause blood clotting in the patient’s legs and lungs, as well as heart attacks and strokes. Inform your health team if you experience any problems with sudden swelling, pain or tenderness in the arms or legs. Patients experiencing chest pain, sudden shortness of breath, vision problems, weakness, seizures or difficulty talking, must seek immediate emergency help. These symptoms caused by blood clots.
Throughout a patient’s treatment with targeted therapy drugs, their health care team will closely monitor them for any possible side effects. Any side effects can and should be treated as quickly as possible. And patient’s experiencing any side effects should inform their health care team about any new or unusual changes. The sooner health providers are informed, the sooner they can treat any possible side effects and keep them from getting worse. Overall, side effects from targeted therapy are manageable and are generally less severe than with traditional chemotherapy treatment.
Challenges of Targeted Therapies
While the idea of targeting a drug to a tumor seems straight forward, this therapy is complex and not always effective. Sometimes the target in the cancer cell may wind up not being as important as was originally thought, so the drug will not provide much of a benefit to the patient. A patient’s cancer may also become resistant to the treatment. Where the targeted therapy worked at first, it may not longer be effective.
While the development of these targeted therapies are a breakthrough in treating cancer, only a few cancers can still be eliminated with just these drugs alone. With a few exceptions, patients with cancer generally receive targeted therapy as part of a combination with surgery, chemotherapy, radiation or hormonal therapy. As physicians learn more about the specific changes in cancer cells, more targeted treatments will be developed.