PARP is an enzyme that helps repair DNA damage. PARP inhibitors are drugs that prevent cancer cells from repairing damaged tumor DNA, which can cause them to die.

PARP inhibitors appear to hold the most promise for people who have a BRCA1 or BRCA2 inherited gene mutation.

BRCA1 and BRCA2-related breast cancers have trouble repairing tumor DNA. These breast cancers seem to be sensitive to DNA damage caused by PARP inhibitors. Treating BRCA1 and BRCA2-related breast cancers with a PARP inhibitor makes it even harder for the breast cancer to repair itself, leading to tumor cell death.

The PARP inhibitor olaparib, or Lynparza, is a treatment for people with HER2-negative early breast cancer who have a BRCA1 or BRCA2 inherited gene mutation, are at high risk of recurrence and have been treated with chemotherapy. Since olaparib is only used to treat people who have a BRCA1 or BRCA2 mutation, you’ll need to get genetic testing if olaparib is being considered in your treatment plan.

Study findings have shown that people with a BRCA1 or BRCA2 gene mutation who had HER2-negative breast cancer at high risk of recurrence and got olaparib had better survival than those who didn’t get olaparib.

Olaparib is a pill taken twice a day, usually for one year after completing chemotherapy.

Some possible side effects of olaparib include anemia, or low red blood cell counts, low white blood cell counts, nausea, vomiting and fatigue. In rare cases, it can cause acute myeloid leukemia.

Once you begin treatment with a PARP inhibitor, and throughout the time you’re taking it, let your health care team know how you’re feeling. They may be able to treat many of these side effects.

For more information, visit the PARP Inhibitors page within the Treatment section of komen.org.

Olaparib is also used to treat HER2-positive metastatic breast cancer. For more information, see the Living with Metastatic Breast Cancer chapter of this tool.