A CDK4/6 inhibitor tablet for hormone-receptor-positive breast cancer
Abemaciclib
A targeted tablet used with hormone therapy for some hormone-receptor-positive, HER2-negative breast cancers.
What is Abemaciclib?
Abemaciclib is a targeted cancer medicine called a CDK4/6 inhibitor, used for certain hormone-receptor-positive, HER2-negative breast cancers, usually alongside hormone therapy. It works by blocking proteins that cancer cells use to grow and divide, so the cancer is slowed down. It is taken by mouth, often twice a day, and is continued for as long as it is helping. The most common problems are diarrhoea and a drop in white blood cells; it can also raise the risk of blood clots and, rarely, cause lung inflammation, so it needs regular monitoring under specialist care.
Education and reference only. This is a plain-language guide to Abemaciclib — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Abemaciclib is a targeted cancer treatment known as a CDK4/6 inhibitor. It is used for some kinds of breast cancer that are hormone-receptor-positive and HER2-negative, where the cancer cells are driven by hormones such as oestrogen. It is taken by mouth and is usually given together with a hormone-blocking medicine, either to treat advanced disease or to lower the chance of an early breast cancer coming back. It is prescribed and supervised by a cancer specialist team, who decide how long it is taken and watch closely for side effects.
How it works
Cancer cells grow by copying themselves, and to do this they rely on proteins called CDK4 and CDK6 that help push the cell through its growth cycle. Abemaciclib blocks these proteins, which stalls the cells before they can divide, so the cancer grows more slowly or shrinks. Because hormone-receptor-positive breast cancers are also fed by hormones, abemaciclib is paired with hormone therapy so the two work together. It is taken every day on a continuous basis, rather than in on-and-off cycles, for as long as it keeps the cancer under control and is tolerated.
Company & origin
Originated / developed by: Specialist manufacturer.
A targeted cancer medicine used in the UK for certain types of hormone-receptor-positive, HER2-negative breast cancer, taken alongside hormone therapy.
Practical use
How to take Abemaciclib
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth as prescribed, usually twice a day at about the same times, with or without food.
- Swallow the tablets whole with water and do not chew, crush or split them.
- Start the anti-diarrhoea medicine you are given at the first sign of loose stools, and keep your fluids up.
- Do not eat or drink grapefruit or grapefruit juice, as it can change how the medicine works.
- Keep taking it every day without breaks unless your specialist tells you to pause or stop.
Weighing it up
Advantages & disadvantages of Abemaciclib
Advantages
- A targeted tablet that, with hormone therapy, can slow advanced breast cancer or lower the chance of early cancer returning.
- Taken by mouth at home rather than as an infusion.
- Works in a different way from chemotherapy, focusing on proteins that drive cancer-cell growth.
Disadvantages
- Diarrhoea is common and can start early in treatment.
- Lowers white blood cells and can raise the risk of blood clots, so monitoring is needed.
- Rarely can cause lung inflammation, and it is not suitable in pregnancy.
Practical use
Good to know
The most common and predictable side effect is diarrhoea, which often starts in the first weeks; the specialist team usually gives an anti-diarrhoea medicine to keep on hand and advice to start it at the first loose stool and to keep up fluids. Abemaciclib also lowers white blood cells, which fight infection, so blood counts are checked regularly and any fever or sign of infection should be reported urgently. It can raise the risk of blood clots in the legs or lungs, so sudden leg swelling, chest pain or breathlessness needs prompt attention. Rarely it can cause inflammation of the lungs, so a new or worsening cough or breathlessness should be reported. Liver blood tests are also monitored. As with all targeted cancer medicines of this kind, it can harm a developing baby, so effective contraception is needed during treatment and for a time afterwards.
Who should not take it / use with caution
- People who have had a serious allergic reaction to abemaciclib should not take it.
- It must not be used in pregnancy, as it can harm a developing baby, and effective contraception is needed during treatment and for a time after.
- It is used with care, and with dose review, in people with significant liver problems or a history of blood clots.
- It should only be used under specialist cancer care with regular blood monitoring.
Monitoring
- Regular blood counts to check white blood cells and watch for infection risk.
- Liver blood tests during treatment.
- Watching for signs of blood clots and for any new cough or breathlessness that could suggest lung inflammation.
Side effects
- Diarrhoea, which is common and often starts in the first weeks.
- A drop in white blood cells, increasing the risk of infection, and tiredness or nausea.
- Blood clots in the legs or lungs, which need prompt medical attention.
- Rarely, inflammation of the lungs or changes in liver blood tests, which need to be reported.
Key interactions
- Grapefruit and some antifungal and antibiotic medicines can raise its levels, so tell your team about everything you take.
- Some medicines, including certain epilepsy treatments and the herbal remedy St John's wort, can lower its levels and reduce how well it works.
- Care is needed with other medicines that affect the liver or increase the risk of blood clots.
Available as: Tablets taken by mouth.
Answers
Abemaciclib: frequently asked questions
What is abemaciclib used for?
It is a targeted medicine used with hormone therapy for certain hormone-receptor-positive, HER2-negative breast cancers, either to treat advanced disease or to lower the chance of early cancer returning.
Why does it cause diarrhoea?
Diarrhoea is a common effect, often in the first weeks; your team usually gives you an anti-diarrhoea medicine to start at the first loose stool, along with advice to keep your fluids up.
Why do I need blood tests?
It can lower the white blood cells that fight infection and affect liver blood tests, so regular monitoring helps catch problems early and adjust treatment if needed.
Can I drink grapefruit juice?
No. Grapefruit and grapefruit juice can change how the medicine is handled by the body, so they should be avoided while taking it.
Is it safe in pregnancy?
No. It can harm a developing baby, so effective contraception is needed during treatment and for a time afterwards; discuss any pregnancy plans with your specialist.
Authoritative sources
- BNF
- NICE CKS
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