PARP inhibitors

PARP inhibitors are a type of targeted cancer drug. They are a treatment for several types of cancer including ovarian, breast and prostate cancer. They are also in trials as a treatment for other types of cancer.

Examples of PARP inhibitors include:

• olaparib
• niraparib
• rucaparib
• talazoparib 

How do PARP inhibitors work?

PARP is a protein (enzyme) found in our cells, it stands for poly-ADP ribose polymerase. It helps damaged cells to repair themselves.

As a cancer treatment, PARP inhibitors stop the PARP from doing its repair work in cancer cells and the cell dies.

Researchers first looked at these drugs in cancers that already had problems repairing cell damage. They focused on cancers with a change (mutation) in genes called BRCA. BRCA stands for BReast CAncer gene.

Normally, BRCA1 and BRCA2 genes stop cells in our body from growing and dividing out of control. If there is a fault (mutation) in these genes, it means that cells can grow out of control. People who have faulty BRCA genes have an increased risk of certain cancers including:

• breast cancer

• ovarian cancer

• prostate cancer

BRCA1 and BRCA2 gene faults are not common. Only around 1 in every 450 people have a faulty BRCA1 or BRCA2 gene.

Cancer cells with BRCA gene faults already have a poor repair system. So blocking PARP with a PARP inhibitor drug means that the cells are not able to repair themselves and they die.

When do you have PARP inhibitors?

PARP inhibitors are a treatment for the following types of cancer:

• breast cancer
• ovarian cancer
• fallopian tube cancer
• peritoneal cancer
• prostate cancer

Researchers think that they might work in cancers that have weaknesses in the cell similar to the BRCA gene fault. There are trials to find whether they are useful in other types of cancer including:

• lung cancer
• pancreatic cancer
• head and neck cancer
• a type of brain tumour called glioblastoma 
• cancer of the stomach and food pipe (oesophagus)
• womb and cervical cancer
• kidney cancer
• children and young people whose cancer has come back 

In some of these trials you have a PARP inhibitor on its own. Or you might have it in combination with other treatments, such as chemotherapy, radiotherapy or another targeted drug.  

Go to Cancer Research UK’s clinical trials database if you are looking for a trial looking into PARP inhibitors in the UK. You will need to talk to your specialist if there are any trials that you think you might be able to take part in.

How you have PARP inhibitors

You usually take PARP inhibitors as tablets or capsules once or twice a day. How often you have them and how long you have treatment will depend on:

• which drug you have

• the type of cancer you have

Side effects of PARP inhibitors

All treatments can cause side effects. While there are general side effects for a type of treatment, they vary for each individual drug and from person to person. The side effects can also depend on what other treatments you’re having.

Tell your doctor or nurse if you have any of these side effects. You might be able to have medicines to help control them.

Common side effects of PARP inhibitors include:

• an increased risk of infection, bleeding problems, tiredness and breathlessness due to a drop in the number of blood cells
• feeling or being sick
• tiredness
• diarrhoea
• indigestion and taste changes
• headaches and dizziness

For more information about the side effects of your treatment, go to the individual drug pages.