Key points
- Abemaciclib is a targeted tablet taken every day, twice a day, for hormone receptor-positive, HER2-negative breast cancer: after surgery in people at high risk of recurrence, and in advanced disease [1].
- In a large study, adding 2 years of abemaciclib to hormone tablets in high-risk patients made the cancer come back less often: of every 10 women whose cancer would have returned without it, about 3 were spared a recurrence [1, 2].
- At 5 years of follow-up the benefit had grown further [3].
- Diarrhoea is the most common side effect and mostly happens in the first month; start an anti-diarrhoea medicine (such as loperamide) at the first loose stool and drink more fluids [1].
- Blood clots, low white blood cells, liver problems and lung inflammation are serious side effects that need monitoring [1].
What is this drug and how does it work?
For physicians
Abemaciclib (brand name Verzenio) is a kinase inhibitor that blocks the cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) [1]. In oestrogen receptor-positive breast cancer cells, cyclin D1 and CDK4/6 drive the cell cycle and cell proliferation by phosphorylating the retinoblastoma protein (Rb) [1].
In laboratory studies, continuous exposure to abemaciclib inhibited Rb phosphorylation, blocked progression from G1 into S phase and led to senescence and apoptosis [1]. Abemaciclib was first approved in the United States in 2017, and its label also includes use as a single agent (without endocrine therapy) [1].
Which cancers is it used for?
Your doctor may prescribe this drug for:
- Early hormone receptor-positive, HER2-negative breast cancer that has spread to the lymph nodes and has a high risk of coming back [1, 2, 3]
- Advanced or spread hormone receptor-positive, HER2-negative breast cancer [1, 4, 5]
- Advanced ER-positive / HER2-negative breast cancer with an ESR1 mutation [1, 6]
- Advanced hormone receptor-positive, HER2-negative breast cancer [1, 7]
Whether it suits you depends on the type and stage of your cancer and your test results. Details of each use are in the section for doctors.
For physicians
| Cancer | Setting | Key evidence |
|---|---|---|
| Early HR-positive / HER2-negative breast cancer with nodal involvement and a high risk of recurrence | Adjuvant treatment with tamoxifen or an aromatase inhibitor for 2 years | monarchE, cohort 1 (4 or more positive nodes, or 1 to 3 nodes with grade 3 or a tumour of 5 cm or more; 5120 patients): HR for invasive disease-free survival 0.65; at 48 months 85.5% vs 78.6% [1, 2]; at the 5-year analysis HR 0.680 [3] |
| Advanced or metastatic HR-positive / HER2-negative breast cancer | With an aromatase inhibitor as initial endocrine-based therapy | MONARCH 3 (493 postmenopausal women): median progression-free survival 28.2 vs 14.8 months (HR 0.54); the overall survival difference (66.8 vs 53.7 months) was not statistically significant [1, 4] |
| Advanced or metastatic HR-positive / HER2-negative breast cancer | With fulvestrant after disease progression on endocrine therapy | MONARCH 2 (669 patients): median progression-free survival 16.4 vs 9.3 months (HR 0.55); median overall survival 46.7 vs 37.3 months (HR 0.76) [1, 5] |
| Advanced ER-positive / HER2-negative breast cancer with an ESR1 mutation | With imlunestrant after progression on at least one line of endocrine therapy | EMBER-3, exploratory analysis of patients with an ESR1 mutation: median progression-free survival 11.1 months with the combination vs 5.5 months with imlunestrant alone (HR 0.53) [1, 6] |
| Advanced HR-positive / HER2-negative breast cancer | Monotherapy after prior endocrine therapy and chemotherapy in the metastatic setting | MONARCH 1 (single-arm trial, 132 patients): objective response 20% by investigator and 17% by independent review [1, 7] |
HR: hazard ratio; a value below 1 means a lower risk of the event.
How it is taken and dosing
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Treatment regimens and doses: index3 regimens
Abemaciclib is a tablet taken twice a day, at about the same times every day, with no break weeks [1]. You can take it with or without food. Swallow the tablet whole; do not chew, crush or split it, and do not take a broken or cracked tablet [1].
If you miss a dose, do not make it up; take the next dose at the usual time. If you vomit after a dose, do not take an extra one [1]. In early breast cancer, treatment continues until 2 years are completed (or until recurrence or side effects that cannot be tolerated); in advanced disease, until the cancer grows or side effects cannot be tolerated [1]. Premenopausal women, and men taking abemaciclib with an aromatase inhibitor, imlunestrant or fulvestrant, also need a GnRH agonist [1]. Keep an anti-diarrhoea medicine at home from the first day and do not stop the drug on your own.
- Dose reduction levels: in combination 150 → 100 → 50 mg twice daily; as monotherapy 200 → 150 → 100 → 50 mg twice daily. If 50 mg twice daily is not tolerated, discontinue permanently [1].
- Monitoring: CBC and ALT, AST and bilirubin before starting, every 2 weeks for the first 2 months, monthly for the next 2 months and then as clinically indicated [1].
- Haematological toxicity: grade 3: hold until grade ≤2, no dose reduction; recurrent grade 3 or grade 4: hold until grade ≤2 and resume at the next lower dose. If G-CSF is needed, wait at least 48 hours after its last dose and until recovery to grade ≤2, then resume at the next lower dose [1].
- Diarrhoea: start antidiarrhoeals and fluids at the first loose stool. Grade 2 not resolving to ≤1 within 24 hours: hold until recovery (no dose reduction); persistent or recurrent grade 2 at the same dose, or grade 3 to 4 or requiring hospitalisation: hold until grade ≤1 and resume at the next lower dose [1].
- Hepatotoxicity: persistent or recurrent grade 2, or grade 3 (without bilirubin above 2 times the upper limit): hold until grade 1 or baseline and resume at the next lower dose. AST/ALT above 3 times with bilirubin above 2 times the upper limit (without cholestasis), or grade 4: discontinue permanently [1].
- ILD/pneumonitis: persistent or recurrent grade 2 (not resolving within 7 days): hold and resume at the next lower dose; grade 3 or 4: discontinue permanently [1].
- Venous thromboembolism: in early breast cancer at any grade, and in advanced disease at grade 3 or 4: hold, treat and resume once clinically stable [1].
- Other toxicities: persistent grade 2 (more than 7 days) or grade 3 to 4: hold until grade ≤1 and resume at the next lower dose [1].
- CYP3A interactions: avoid ketoconazole. With other strong CYP3A inhibitors, reduce to 100 mg twice daily (or to 50 mg if already reduced to 100 mg), and return to the previous dose after the inhibitor is stopped (after 3 to 5 half-lives). With moderate inhibitors, monitor and reduce by 50 mg if needed. Avoid strong and moderate CYP3A inducers [1].
- Liver and kidney: severe hepatic impairment (Child-Pugh C): same dose once daily. Mild and moderate renal impairment (CLcr 30 to 89 mL/min): no adjustment; no data for CLcr below 30 or dialysis [1].
- Creatinine: the rise in serum creatinine (mean 0.2 to 0.3 mg/dL, in the first cycle, reversible on stopping) is caused by inhibition of tubular secretion and does not reflect a fall in GFR; use measures not based on creatinine (such as BUN or cystatin C) to assess kidney function [1].
For physicians
Standard dosing (FDA label)
Abemaciclib + endocrine therapy (adjuvant)
Early HR-positive, HER2-negative, node-positive breast cancer at high risk of recurrence
Early HR-positive, HER2-negative, node-positive breast cancer at high risk of recurrence
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Abemaciclib | 150 mg twice daily | Oral | Every day, continuously |
| Tamoxifen or an aromatase inhibitor | As per that drug's label | Oral | Every day |
Pre- or perimenopausal women and men receiving an aromatase inhibitor should also receive a GnRH agonist [1].
Abemaciclib + an aromatase inhibitor, fulvestrant or imlunestrant
Advanced or metastatic HR-positive, HER2-negative breast cancer: first line with an aromatase inhibitor; after progression on endocrine therapy with fulvestrant; with imlunestrant only with an ESR1 mutation (FDA-approved plasma test) after at least one line of endocrine therapyCycle length: Continuous
Advanced or metastatic HR-positive, HER2-negative breast cancer: first line with an aromatase inhibitor; after progression on endocrine therapy with fulvestrant; with imlunestrant only with an ESR1 mutation (FDA-approved plasma test) after at least one line of endocrine therapy
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Abemaciclib | 150 mg twice daily | Oral | Every day, continuously |
| Partner endocrine drug | As per that drug's label |
Pre- or perimenopausal women and men taking an aromatase inhibitor, fulvestrant or imlunestrant need a GnRH agonist [1].
Abemaciclib monotherapy
Advanced HR-positive, HER2-negative breast cancer progressing after endocrine therapy and prior chemotherapy in the metastatic settingCycle length: Continuous
Advanced HR-positive, HER2-negative breast cancer progressing after endocrine therapy and prior chemotherapy in the metastatic setting
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Abemaciclib | 200 mg twice daily | Oral | Every day, continuously |
Dose reduction levels: 150, then 100, then 50 mg twice daily [1].
Doses follow the trial protocol, guideline or official drug label (source given in the notes of each regimen). Before prescribing, check blood counts, renal and hepatic function, drug interactions and the patient’s condition, and adjust the dose according to the drug label.
Side effects
The most common side effects:
- Diarrhoea: in most patients, usually in the first week [1]. At the first loose stool, take the anti-diarrhoea medicine your doctor gave you and drink plenty of fluids [1].
- Low white blood cells: in most patients; it only shows up in blood tests but raises the risk of infection [1].
- Anaemia, infections and tiredness [1].
- Nausea or vomiting, headache, mouth sores, skin rash and mild hair thinning [1].
For physicians
| Adverse reaction | Frequency (all grades) | Grade 3 or 4 |
|---|---|---|
| Diarrhoea | 84% | 8% [1] |
| Decreased neutrophils (laboratory) | 84% | 18% grade 3, 0.7% grade 4 [1] |
| Decreased haemoglobin (laboratory) | 68% | 1% [1] |
| Decreased lymphocytes (laboratory) | 59% | 13% grade 3, 0.2% grade 4 [1] |
| Infections | 51% | 4.9% grade 3, 0.6% grade 4 [1] |
| Fatigue | 41% | 2.9% [1] |
| Increased ALT (liver enzyme) | 37% | 2.5% grade 3 [1] |
| Decreased platelets (laboratory) | 37% | 0.7% grade 3, 0.2% grade 4 [1] |
| Nausea / vomiting | 30% / 18% | 0.5% / 0.5% [1] |
| Headache | 20% | 0.3% [1] |
| Stomatitis | 14% | 0.1% [1] |
| Rash / alopecia | 11% each | 0.4% / 0 [1] |
Increased serum creatinine was seen in 99% of patients (vs 91% with endocrine therapy alone) and usually does not reflect kidney damage [1]. Decreased appetite occurred in 12% (grade 3 or 4: 0.6%) [1]. Other clinical adverse reactions below 10%: pruritus (9%), dyspepsia (8%), nail changes (6%), increased lacrimation (6%), ILD/pneumonitis (3%) and venous thromboembolism (3%) [1].
Serious side effects
These are less common but serious; tell your team early if you notice any sign of them:
- Severe diarrhoea with dehydration (great thirst, dizziness, passing little urine) [1].
- Fever or chills, because your white blood cells may be low [1].
- Lung inflammation: a new cough, shortness of breath or chest pain; in about 3 in 100 people [1].
- Liver damage: usually causes no symptoms and is found with regular blood tests; report yellow skin or eyes straight away [1].
- Blood clots: pain or swelling in one leg, or sudden shortness of breath; in 2 to 5 in 100 people [1].
- Harm to an unborn baby; do not become pregnant during treatment [1].
For physicians
The FDA label has no boxed warning but lists these warnings [1]:
- Severe diarrhoea: reported with dehydration and infection. Across five trials (3899 patients), diarrhoea occurred in 81 to 90% and grade 3 diarrhoea in 8 to 20% of patients; median time to onset was 6 to 8 days [1].
- Neutropenia: in 37 to 51% of patients; grade 3 or higher decreased neutrophils in 19 to 32%. Febrile neutropenia occurred in less than 1%, and two deaths from neutropenic sepsis were reported in MONARCH 2 [1].
- Interstitial lung disease (ILD) and pneumonitis: 3% in monarchE (0.4% grade 3 or 4 and one fatal case) and 3.2% in advanced disease (0.5% grade 3 or 4 and 0.5% fatal) [1].
- Hepatotoxicity: grade 3 or higher ALT increase in 2 to 6% and AST increase in 2 to 3% of patients [1].
- Venous thromboembolism: deep vein, pulmonary and other venous clots in 2 to 5% of patients, including deaths. Abemaciclib has not been studied in early breast cancer patients with a history of clots [1].
- Embryo-fetal toxicity [1].
When should I call my doctor?
Contact your treatment team straight away if you have [1]:
- Diarrhoea: start the anti-diarrhoea medicine at the first loose stool, drink more fluids and tell your doctor, especially if it does not improve within 24 hours
- Fever, chills or signs of infection
- Pain or swelling of an arm or leg, sudden shortness of breath, chest pain, fast breathing or a fast heartbeat (possible signs of a blood clot)
- A new or worsening cough or shortness of breath
- Yellow skin or eyes, dark urine or pain in the upper right abdomen
- A possible pregnancy
Interactions, pregnancy and precautions
- Other medicines: antifungal drugs such as ketoconazole raise abemaciclib levels in the blood a lot and must not be taken with it; with some other medicines the abemaciclib dose may need to be lowered [1]. Medicines such as rifampicin (a tuberculosis drug) and epilepsy medicines reduce its effect [1].
- Grapefruit: grapefruit and grapefruit products may raise the drug level in the blood; avoid them during treatment [1].
- Pregnancy: pregnancy is checked before starting. Women who could become pregnant should use effective contraception during treatment and for 3 weeks after the last dose; with combination treatment, the longest period recommended in the partner drugs' leaflets applies [1].
- Breastfeeding: do not breastfeed during treatment and for 3 weeks after the last dose [1].
- Male fertility: based on animal studies, abemaciclib may reduce male fertility [1].
- If you have had a blood clot, tell your doctor before starting [1]. Tell your doctor about all your medicines, including over-the-counter medicines, vitamins and herbal products [1].
Frequently asked questions
Why do I need an anti-diarrhoea medicine at home from day one?
For how many years do I take abemaciclib after surgery?
In high-risk early breast cancer, abemaciclib is taken with hormone therapy until 2 years are completed [1]. Hormone therapy continues as your doctor plans.
My blood creatinine has gone up; does that mean my kidneys are damaged?
What should I do if I forget a dose?
Do not make up the missed dose; take the next dose at the usual time [1].
Can I eat grapefruit?
No. Grapefruit may raise the level of abemaciclib in the blood and increase side effects [1].
Scientific evidence
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Key studies
2 itemsBreast Cancer, Version 4.2026, NCCN Clinical Practice Guidelines In Oncology
Adjuvant Abemaciclib Plus Endocrine Therapy for Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative, High-Risk Early Breast Cancer: Results From a Preplanned monarchE Overall Survival Interim Analysis, Including 5-Year Efficacy Outcomes
Related cancer types
References
7 referencesShow all references, 6 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1VERZENIO (abemaciclib) tablets — Prescribing Information
- 2Abemaciclib Combined With Endocrine Therapy for the Adjuvant Treatment of HR+, HER2−, Node-Positive, High-Risk, Early Breast Cancer (monarchE)
- 3Adjuvant Abemaciclib Plus Endocrine Therapy for Hormone Receptor–Positive, Human Epidermal Growth Factor Receptor 2–Negative, High-Risk Early Breast Cancer: Results From a Preplanned monarchE Overall Survival Interim Analysis, Including 5-Year Efficacy Outcomes
- 4MONARCH 3: Abemaciclib As Initial Therapy for Advanced Breast Cancer
- 5MONARCH 2: Abemaciclib in Combination With Fulvestrant in Women With HR+/HER2− Advanced Breast Cancer Who Had Progressed While Receiving Endocrine Therapy
- 6Imlunestrant with or without Abemaciclib in Advanced Breast Cancer
- 7MONARCH 1, A Phase II Study of Abemaciclib, a CDK4 and CDK6 Inhibitor, as a Single Agent, in Patients with Refractory HR+/HER2− Metastatic Breast Cancer
This page is based on reputable scientific sources and was last updated on 27 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
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