PARP is an enzyme that helps repair DNA damage. PARP inhibitors are drugs that try to keep cancer cells from repairing damaged tumor DNA.

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 problems 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 used to treat HER2-negative early breast cancer at high risk of recurrence in people who have a BRCA1 or BRCA2 inherited gene mutation 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 people with a BRCA1 or BRCA2 gene mutation who had HER2-negative breast cancer at high risk of recurrence and got olaparib had a lower risk of breast cancer recurrence than those who didn’t get olaparib.

Olaparib is a pill. It’s taken twice a day, every day for a year. You start taking olaparib after you’ve completed chemotherapy.

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

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