abemaciclib
Verzenio (abemaciclib) is an oral CDK4/6 inhibitor from Eli Lilly. It blocks cyclin-dependent kinases 4 and 6, keeps the retinoblastoma (Rb) protein unphosphorylated, and arrests cancer cells in the G1 phase before they can replicate their DNA. It is used, mostly alongside endocrine therapy, in hormone receptor-positive, HER2-negative breast cancer.
This page is based on the official US label for VERZENIO and the EMA product information for Verzenios, cross-checked against MedlinePlus and the NCI Drug Dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
A cell about to divide is like a car at the start line, and CDK4 and CDK6 are the two ignition keys that let it pull away. In many breast cancers those keys keep turning over and over. Abemaciclib pockets both keys, so the car stays parked at the start line (the G1 phase) instead of racing into copying its DNA.
In simple terms
Breast cancer cells grow because molecular "accelerators" called CDK4 and CDK6 keep telling them to divide. Abemaciclib is a kinase inhibitor that switches those accelerators off. Without them, cancer cells cannot pass the checkpoint where they prepare to copy their DNA, so they stop multiplying and gradually die off. That is why it works best in cancers driven by hormones, and why it is usually paired with hormone-blocking treatment.
In depth
Abemaciclib selectively inhibits cyclin-dependent kinases 4 and 6. When complexed with D-type cyclins, CDK4/6 phosphorylate the retinoblastoma (Rb) protein, releasing E2F transcription factors and licensing the G1-to-S phase transition. By preventing Rb phosphorylation, abemaciclib arrests cells in G1, suppresses DNA synthesis, and induces senescence and apoptosis in tumor cells. In ER-positive breast cancer, estrogen signaling upregulates cyclin D1, which is why combining CDK4/6 inhibition with endocrine therapy is synergistic.
Target: Cyclin-dependent kinases 4 and 6 (CDK4/6)
Kinases activated by D-type cyclins that drive the cell cycle from the G1 phase into the S phase; in hormone receptor-positive breast cancer they are overactive and push cells to keep dividing.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDAas of Jul 13, 2026- With endocrine therapy (tamoxifen or an aromatase inhibitor), for the adjuvant treatment of adults with HR-positive, HER2-negative, node-positive early breast cancer at high risk of recurrence
- With an aromatase inhibitor as initial endocrine-based therapy for HR-positive, HER2-negative advanced or metastatic breast cancer
- With fulvestrant for HR-positive, HER2-negative advanced or metastatic breast cancer that has progressed after endocrine therapy
- On its own for HR-positive, HER2-negative advanced or metastatic breast cancer that has progressed after endocrine therapy and prior chemotherapy in the metastatic setting
Approved uses in European Union
EMAas of May 27, 2026- Early breast cancer: with endocrine therapy, for the adjuvant treatment of adults with HR-positive, HER2-negative, node-positive early breast cancer at high risk of recurrence; in pre- or perimenopausal women the aromatase inhibitor should be combined with an LHRH agonist
- Advanced or metastatic breast cancer: for women with HR-positive, HER2-negative locally advanced or metastatic disease, with an aromatase inhibitor or fulvestrant, either as initial endocrine-based therapy or after prior endocrine therapy; in pre- or perimenopausal women the endocrine therapy should be combined with an LHRH agonist
Official sources
The statements on this page trace back to these records.
- DailyMed: VERZENIO (abemaciclib) official US label
U.S. National Library of Medicine, DailyMed · Retrieved Aug 22, 2026
- openFDA drug label record for abemaciclib
U.S. Food and Drug Administration, openFDA · Retrieved Aug 22, 2026
- EMA product information: Verzenios (abemaciclib)
European Medicines Agency · Retrieved Aug 22, 2026
- NCI Drug Dictionary: abemaciclib
National Cancer Institute · Retrieved Aug 22, 2026
- MedlinePlus: abemaciclib
MedlinePlus, U.S. National Library of Medicine · Retrieved Aug 22, 2026
Editorial review
- Reviewed
- Aug 22, 2026
- Next review
- Feb 22, 2027
- Cross-checked by
- researcher-regulatory - FDA/DailyMed/EMA labels · researcher-nlm - MedlinePlus/NCI · editor - plain-language paraphrase and cross-check
- Method
- independent multi-source collection -> cross-check for agreement -> original English paraphrase -> item-by-item verification against the evidence bundle
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.