How Are Targeted Therapies Used For Prostate Cancer?
Targeted drug therapies are now being used to treat prostate cancer. Targeted therapy differs from chemotherapy in that chemotherapy affects both cancerous and healthy cells. It is more of a “one size fits all” approach. Targeted therapy drugs interfere with, or target, specific parts of cancer cells. Once the drug finds its target, it latches on and interferes with the cancer’s ability to grow, while helping to lessen the impact on normal, healthy cells.1
What makes a good target?
Good targets are those found in cancer cells but not in healthy cells. This makes it easy for the therapeutic drug to find the cancer. Certain genetic mutations are common targets. Healthy cells and cancerous cells share similar genetic makeup, but the genes of cancer cells can have mutations making them unique. Successful targeted therapy drugs exploit these differences to attack the cancer and leave healthy cells generally undisturbed, helping to minimize side effects.1
Targeted therapies for prostate cancer
Some targeted therapy drugs have been approved by the U.S. Food and Drug Administration (FDA) to treat prostate cancer. Targeted therapies are generally considered cytostatic, meaning they block the growth and division of cancer cells, while chemotherapy is typically considered cytotoxic, meaning it kills cancer cells.1
Poly (ADP-ribose) polymerase (PARP) inhibitors
The purpose of cell growth and division is to pass DNA from one cell to another. When cancer cells divide, their DNA is damaged. The DNA must be fixed or cells die. There are two types of damage that cells must fix:8,10
- Single-stranded damage – DNA breaks in one spot. Cells use PARP to fix it.
- Double-stranded damage – DNA breaks in two spots. There are about 15 genes involved in this repair. As many as 1 out of every 5 men with metastatic (has spread to other parts of the body) prostate cancer may have a mutation in one of these genes. BRCA1 and BRCA2 are 2 genes involved in this pathway. These mutations make prostate cancer more aggressive.
If you have a mutation in, for example, BRCA1 and BRCA2, you cannot use the double-stranded repair pathway. This leaves PARP as the only way to fix DNA. PARP inhibitors like olaparib (Lynparza®) and rucaparib (Rubraca®) target and inhibit PARP. This stops DNA repair and kills cancer cells. If you have a mutation in DNA-repair genes, your doctor may use one of these drugs depending on which mutation you have.8-10
Olaparib may be used for prostate cancer with specific genetic mutations that has spread (metastatic) and is not responding to treatment to lower the body’s level of testosterone (castration-resistant), and has gotten worse after being treated with abiraterone or enzalutamide. Rucaparib may be used for prostate cancer with a specific BRCA mutation that has spread (metastatic) and is not responding to treatment to lower the body’s level of testosterone (castration-resistant), and has previously been treated with taxane chemotherapy and therapy aimed at androgen receptors.1,9-10
Side effects of targeted therapy
Side effects of targeted therapies vary based off your overall health and which therapy you get. Since targeted therapies aim to minimize effect on healthy cells, you may have less symptoms than with chemotherapy. Common side effects of certain targeted therapy drugs may include:1
- Liver problems
- Low blood cell counts
- Feeling tired
- Decreased appetite
- Nausea and vomiting
These are not all the possible side effects of targeted therapies. Talk to your doctor about what to expect or if you experience any changes that concern you during treatment with targeted therapies.1
Long-term use of targeted therapies
Targeted therapies can stop working as time goes on. If you are a candidate for a targeted therapy drug, you may be asked to switch therapies, add one, or use with chemotherapy. Targeted therapy drugs are a powerful tool in the fight against prostate cancer. However, the development process is extensive, so advances in this field take time. Talk to your doctor if you are interested in learning more about targeted therapy drugs.1