What Are PARP Inhibitors?
If you’ve been diagnosed with breast cancer that is HER2-negative and have a BRCA1 or BRCA2 mutation, you may be prescribed a PARP inhibitor. PARP inhibitors are a type of targeted therapy. They work by targeting a protein called poly ADP-ribose polymerase (PARP). PARP inhibitors are also used to treat some ovarian cancers.
Currently there are two approved PARP inhibitors used to treat breast cancer:
Both Lynparza and Talzenna are pills taken by mouth. Talzenna is a pill you take once daily, while Lynparza is taken twice a day. Both can be taken with or without food.
Another PARP inhibitor, named veliparib, is being tested in clinical trials. Studies suggest that people with BRCA1/2 mutations who have metastatic HER2-negative breast cancer who take veliparib after chemotherapy may have better outcomes than those who receive chemo only. Veliparib has not been approved by the FDA.
How do PARP inhibitors work?
When healthy and cancerous cells are damaged, they rely on helper compounds like PARP proteins and BRCA1/2 proteins to fix things so the cells can continue growing. In cancer with a BRCA mutation, BRCA can’t fix things the way it normally does, so cancer cells rely more on PARP for support. PARP inhibitors disrupt PARP’s function, leaving cancer cells with no repair help. These cells then become too damaged and die.
Who is prescribed PARP inhibitors?
Your treatment team can help you decide which PARP inhibitor is right for you.
You may be prescribed Lynparza if you have HER2-negative breast cancer that has spread to other areas of the body (called metastatic breast cancer), you have a BRCA1/2 mutation, and you’ve been treated with chemotherapy.
Talzenna is also used as an alternative to chemotherapy for people with a BRCA1/2 mutation and HER2-negative breast cancer that has spread to tissue near the breast (called locally advanced) or other areas of the body.
You may be prescribed Lynparza for early-stage breast cancer if there’s a high risk the cancer could come back (called breast cancer recurrence) and you’ve completed chemotherapy and surgery. Research suggests that people with early-stage breast cancer who take Lynparza for one year after completing standard treatment are less likely to have breast cancer come back years later.
Side effects of PARP inhibitors
Like all cancer therapies, there are side effects associated with taking PARP inhibitors. The most common side effects of Lynparza and Talzenna are:
If you’re taking a PARP inhibitor, you’ll likely get blood tests at least monthly so your doctor can track your complete blood counts during treatment. While low red and white blood cell counts are common side effects of both Lynparza and Talzenna, they can also be symptoms of:
myelodysplastic syndrome, a disorder in which immature blood cells in blood marrow do not become healthy blood cells
acute myeloid leukemia, a type of blood and bone marrow cancer
Tell your doctor right away if you have:
blood in your urine or stool
extreme tiredness
frequent infections
bruising or bleeding more easily
These are not all of the potential side effects of PARP inhibitors. Keep in mind that side effects from Lynparza and Talzenna can vary widely from person to person.
There are a few other things to consider about PARP inhibitors if you’re pregnant or breastfeeding, or if you or your partner could become pregnant.
PARP inhibitors can harm a developing baby and may cause loss of pregnancy (miscarriage). If you’re able to become pregnant, you’ll be advised to use birth control while taking PARP inhibitors and for at least six (Lynparza) or seven (Talzenna) months after the last dose of medication. You may be asked to take a pregnancy test before and during treatment.
If you have a partner who is pregnant or able to become pregnant, effective birth control is recommended during treatment and for at least three (Lynparza) or four (Talzenna) months after the last dose of medication. People are also advised not to donate sperm during treatment or for at least three months after.
It’s not known if PARP inhibitors pass into breast milk, but it’s not recommended to breastfeed during treatment and for at least one month after the last dose of either Lynparza or Talzenna.
More research is needed to understand the effects of PARP inhibitors on fertility. Research is farther along for people with prostates — for example, animal studies suggest Talzenna may reduce fertility in people with prostates. Less is known about the effects of Lynparza on fertility in people with or without prostates. If you’re concerned and considering having children, talk with your doctor about fertility preservation options.
Tips for taking PARP inhibitors
Be aware of potential side effects, when you need to take the pill(s), what to do if you miss a dose, and whether any other medications you’re taking might interact with the PARP inhibitor. Be sure to track your side effects and alert your healthcare team so they can help you find relief.
Both Lynparza and Talzenna prescriptions can’t be filled at a normal pharmacy. They’re normally ordered through a specialty pharmacy that carries medications for more complex medical conditions like breast cancer. Discuss with your treatment team how and where you’ll get your initial medications and refills.
It’s important to continue taking any other medication your treatment team wants you to take, like hormonal therapy if you’ve been diagnosed with hormone receptor-positive breast cancer that has not spread. You may find it helpful to organize your different medications using a pill organizer. Stay on track with your medication schedule by using different timers or reminders.
PARP inhibitors lower white blood cell counts, which can increase your risk of infection. During treatment, your immune system won’t be at full strength. Use hand sanitizer and wash your hands often, avoid large crowds, and stay away from people who may be sick.
Avoid these fruits during treatment, as they can increase the level of the PARP inhibitor in your blood.
Research shows that exercise can help ease fatigue, a common side effect of PARP inhibitors. Try to build a schedule during your treatment that includes light exercise and rest.
Nausea and vomiting are common side effects of these medications. Because vomiting can lead to dehydration, it’s a good idea to up the amount of water and fluids you’re drinking during treatment. You may also want to adjust your eating habits by eating smaller, more frequent meals to help with the nausea.
Why PARP inhibitors may stop working
Breast cancer cells often figure out how to work around PARP inhibitors and grow (this is called becoming resistant). When this happens, the drugs stop working and the cancer comes back. It’s estimated that between 40% and 70% of people who take PARP inhibitors will develop resistance over time.
Researchers are currently working on understanding how cancer cells become resistant to these medicines. Researchers are investigating using other targeted therapies in combination with PARP inhibitors, which could help prevent people from developing resistance to PARP inhibitors.
— Last updated on March 29, 2025 at 2:49 PM