1. What are PARP inhibitors?
PARP inhibitors are a type of targeted therapy.
The most widely used PARP inhibitor is currently olaparib (Lynparza).
Other PARP inhibitors include:
2. Who might be offered PARP inhibitors?
Primary breast cancer
You may be offered olaparib if you have an altered BRCA gene, have had and have that is:
Not everyone with an altered BRCA gene and these types of breast cancer will be offered olaparib. It also depends on factors like the size of the cancer and whether any lymph nodes (glands) are affected.
Secondary breast cancer
If you have or , you may be offered PARP inhibitors (most likely talazoparib).
You may be offered PARP inhibitors if:
- Your locally advanced or secondary breast cancer is HER2-negative
- You have an altered BRCA gene
- You’ve already had certain chemotherapy treatments
Availability
Olaparib is the only PARP inhibitor drug currently available on the NHS for some people with primary breast cancer.
Olaparib and talazoparib are available on the NHS for some people with secondary breast cancer.
Speak with your treatment team to see if these treatments are suitable for you.
3. How PARP inhibitors work
PARP stands for poly-ADP ribose polymerase. It’s a protein that helps cells repair themselves if they become damaged. PARP inhibitors stop the PARP from repairing cancer cells.
If you have an altered BRCA1 or BRCA2 gene, you have an increased risk of developing breast cancer. Cancer cells with altered BRCA genes are less able to repair themselves if they become damaged. PARP inhibitors can also help stop the cancer cells repairing themselves, so they become too damaged to survive.
4. How to take PARP inhibitors
Life during treatment
Going through breast cancer treatment can affect you physically and emotionally. Read our tips to help you cope.
You take PARP inhibitors as tablets or capsules.
If you are taking talazoparib, you will have a tablet or capsule once a day.
If you are taking olaparib, you will have a tablet or capsule twice a day.
Clinical trials have shown you can take PARP inhibitors on their own or alongside hormone (endocrine) therapy. Research is looking into having PARP inhibitors alongside or other targeted therapies.
5. Side effects of PARP inhibitors
Like any treatment, PARP inhibitors can cause side effects. Everyone reacts differently to drugs and some people have more side effects than others. These side effects can usually be managed and those described here will not affect everyone.
You may experience different side effects depending on which PARP inhibitor you have.
Because you may have PARP inhibitors alongside other drugs, you may also experience side effects from these. It’s sometimes difficult to know which drug causes which side effect.
Before starting PARP inhibitors, you should be given a 24-hour contact number or told who to contact if you feel unwell at any time during your treatment, including overnight or at the weekends.
If you’re worried about any side effects, regardless of whether they’re listed here, talk to your treatment team.
Common side effects of PARP inhibitors
Effects on the blood
PARP inhibitors can temporarily affect the number of blood cells in the body. Blood is made up of red cells, white cells and platelets.
You’ll have regular blood tests. If these show the number of blood cells is too low, your next treatment may be delayed or the dose of PARP inhibitors reduced.
Your treatment team may change the dose of a drug to suit you and help manage its side effects. This may help you stay on the treatment for longer.
Risk of infection
Not having enough white blood cells can increase your risk of getting an infection.
Signs of an infection
Your treatment team may give you guidelines to follow for reporting signs of an infection. But generally you should contact your hospital immediately if you have any of the following:
- A high temperature (over 37.5°C) or low temperature (under 36°C)
- Suddenly feeling unwell, even with a normal temperature
- Symptoms of an infection, such as a sore throat, cough, needing to pee often or feeling cold or shivery, even if you do not have a high temperature
Before starting PARP inhibitors, you should be given a 24-hour contact number or told who to contact if you feel unwell at any time during your treatment, including overnight or at the weekends.
You may need treatment if you get an infection.
Sometimes your doctor may recommend injections of drugs called growth factors. This helps the body produce more white blood cells to reduce your risk of infection.
Anaemia
Having too few red blood cells is called anaemia. If you feel breathless, dizzy or particularly tired, let your treatment team know.
Bruising and bleeding
PARP inhibitors can reduce the number of platelets. Platelets help the blood to clot.
If your platelets are low, you may:
- Bruise more easily
- Have nosebleeds
- Notice that your gums bleed when you brush your teeth
- Take longer to stop bleeding if you cut yourself
Tell your treatment team if you have any of these symptoms.
Diet during breast cancer treatment
Learn about how different breast cancer treatments may affect your diet and how you can manage these changes.
Nausea and vomiting
You may feel sick (nausea) or be sick (vomit) at times during your treatment.
Let someone in your treatment team know if you’re feeling sick or being sick. They should be able to give you anti-sickness drugs to help.
Try to eat small regular meals if possible and have regular drinks.
Extreme tiredness (cancer-related fatigue)
Fatigue is extreme tiredness that doesn’t go away with rest or sleep.
If you think you have fatigue, tell your GP or treatment team. They can assess you and offer advice on how to manage your energy levels.
Find out more about managing fatigue.
Dizziness
PARP inhibitors may cause dizziness. Do not drive if you feel dizzy.
If your dizziness doesn’t improve, speak to your treatment team or GP.
Diarrhoea
This is usually mild. If you have diarrhoea, try to drink plenty of fluids. Your treatment team or GP can also give you medication to help.
Contact your treatment team if you have diarrhoea 3 or more times in 24 hours, compared to what’s usual for you.
Other common side effects
Other common side effects of PARP inhibitors include:
- Headaches
- Cough or shortness of breath
- Loss of appetite
- Taste changes
- Heartburn or indigestion
Less common side effects of PARP inhibitors
Liver and kidney changes
PARP inhibitors can affect how your liver and kidneys work.
Your treatment team will arrange regular blood tests while you’re having treatment to check for this.
Damage to the lungs
PARP inhibitors can cause interstitial lung disease (ILD). ILD can cause inflammation in your lungs, which can lead to scarring.
If PARP inhibitors have caused inflammation to your lungs, you may need to stop treatment temporarily to prevent further damage. You may have steroids to treat the inflammation.
Contact your treatment team straight away if you have:
- Shortness of breath
- A cough, with or without a high temperature
- Any new or worsening breathing problems, such as chest tightness or wheezing
These symptoms could have a number of causes including side effects of treatment or a lung infection. It’s important to let your treatment team know so that they can find out the cause. You may need a chest x-ray or CT scan to check what’s causing your symptoms.
Hair loss
The PARP inhibitor talazoparib may cause hair loss or thinning.
Any hair loss should be temporary. For most people, hair will begin to grow back in the weeks and months after treatment has finished.
Read more about hair loss.
Other less common side effects
Other less common side effects of PARP inhibitors include:
- Stomach pain
- Skin rashes
- Sore mouth
6. Other important information
Allergic reaction
Allergic reactions to PARP inhibitors can occasionally happen. Reactions can vary from mild to severe.
If you have an allergic reaction to PARP inhibitors, it’s more likely to happen the first time you have treatment.
Contact your hospital immediately if you notice any of the following symptoms:
- Itchy red or discoloured bumps on your skin (these may be harder to see on black or brown skin)
- Swelling in your lips, tongue or throat
- Breathlessness, wheezing, a bad cough or sudden difficulty breathing
- Tight chest or chest pain
If you have a severe reaction, treatment will be stopped immediately. If you have a less severe reaction, you may need to take medication before future treatments to reduce the risk of further reactions.
Blood clots
People with breast cancer have a higher risk of blood clots. Having PARP inhibitors also increases the risk of blood clots such as a DVT (deep vein thrombosis).
If you have a DVT, there’s a risk part of the blood clot could break away and travel to the lung. This is known as a pulmonary embolism (PE).
Blood clots can be life-threatening and should be treated quickly.
Blood clot symptoms
Contact your treatment team or go to your local A&E department straight away if you have any of the following symptoms:
- Pain in your arm or leg
- Redness/discolouration of the skin of the arm or leg
- Heat and swelling of the arm or leg
- Swelling, redness or tenderness where a central line is inserted to give chemotherapy, for example in the arm, chest area or up into the neck
- Shortness of breath that comes on suddenly
- Pain or tightness in the chest
- Unexplained cough or coughing up blood
Some symptoms may look different on different skin tones.
Find out more about blood clots.
Medicines and food to avoid when having PARP inhibitors
If you’re taking olaparib, you should avoid:
- Eating grapefruit and drinking grapefruit juice
- Eating bitter (Seville) oranges (often found in marmalade)
This is because they can affect how PARP inhibitors work.
There are some drugs you shouldn’t take with PARP inhibitors. It’s important to tell your treatment team about any prescribed or over-the-counter medicines you’re taking.
It’s also important to speak to your treatment team before taking any herbal medicines or supplements. This is because you should not take some herbal medicines and supplements while taking PARP inhibitors. For example, you should not take anything containing St John’s wort if you’re taking some PARP inhibitors.
Sex, contraception and pregnancy
You can still have sex during treatment. It’s thought some drugs used to treat breast cancer cannot pass into vaginal fluids or semen, but this cannot be completely ruled out.
Most treatment teams will advise using barrier methods of contraception, such as condoms or female condoms, during treatment and for a period of time after PARP inhibitors are given.
Check with your treatment team how long you should continue using a barrier method of contraception after your treatment has finished.
You’re advised not to become pregnant while having treatment because PARP inhibitors can harm a developing baby. If you have not been through the menopause, talk to your team about the most suitable method of contraception for you. It’s still possible to become pregnant even if your periods are irregular or have stopped naturally or because of treatment for breast cancer.
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Fertility
We don’t currently know if PARP inhibitors affect fertility, but it is a possibility.
Conversations about fertility can be hard. It’s important to discuss any fertility concerns with your treatment team before you begin your treatment.
If you were diagnosed with locally advanced or secondary breast cancer before you started or completed your family, you may be concerned about your fertility. Depending on your diagnosis and treatment, you may be advised not to get pregnant.
You can talk to your treatment team about any possible fertility preservation options before starting treatment.
You can also talk to our specialist nurses on our free helpline (see below).
Breastfeeding
You should not breastfeed while having PARP inhibitors and for a period of time after the last dose. This is because there’s a risk the drugs can be passed on through breast milk.
Travel and vaccinations
If you’re planning a holiday or need to travel overseas, check with your treatment team first.
You should not have any live vaccines while you’re having treatment.
For more information about vaccines, including COVID-19 and flu vaccines, see our information on vaccines and breast cancer.
7. Further support
If you'd like more information about PARP inhibitors or just want to talk things through, you can speak to our specialist nurses through our free helpline and Ask Our Nurses service (see below).
You can also talk to other people having treatment with PARP inhibitors on our online forum.
If you’re living with secondary breast cancer, we have a range of support available for you through our Living with Secondary Breast Cancer services – see below.
