Abemaciclib (Verzenio)

Abemaciclib (Verzenio) is a targeted therapyinfo-icon approved by the Food and Drug Administrationinfo-icon to treat hormone receptorinfo-icon-positive breast cancer. It is a cyclin-dependent kinase 4/6 (CDK 4/6) inhibitor, which means it targets two specific kinases, or proteins, that help tumorinfo-icon cells reproduce. Those kinases are CDK 4 and CDK 6.

CDK 4/6 inhibitors are relatively new treatments. The first, palbociclib (Ibrance), was approved by the FDAinfo-icon in 2015. Another, ribociclib (Kisqali), was approved in early 2017. Later that year, abemaciclib became the third medicineinfo-icon of this type to be approved for hormone receptor-positive, HER2-negative metastaticinfo-icon breast cancer. In 2021, the FDA expanded the approval of abemaciclib for use in high-risk, early-stage breast cancerinfo-icon. It is the only CDK 4/6 inhibitor approved for use in early-stage breast cancer.

While these three medicines mostly work in the same way, abemaciclib differs slightly from the other two in its dosing. Abemaciclib is taken continuously, whereas palbociclib and ribociclib are given in cycles with breaks.

How abemaciclib works

Cyclin-dependent kinases 4 and 6 are two proteins that help some breast cancers to grow. Medicines like abemaciclib are called CDK 4/6 inhibitors because they block these proteins from signaling cancer cells to multiply, which helps slow the growth or spread of the cancer.

Who gets abemaciclib

Abemaciclib in early-stage breast cancerinfo-icon

Abemaciclib may be given to people with high-risk early-stage breast cancer that is hormoneinfo-icon-receptorinfo-icon positive, HER2-negative. Determining whether a cancer is at high risk for recurrenceinfo-icon depends on different features of the cancer. This includes the number of lymphinfo-icon nodes that have cancer, the size and gradeinfo-icon of cancer, and results of a Ki-67 index test on the tumorinfo-icon.  

Ki-67 is a proteininfo-icon found in cells that affects the way cells divide and grow. Early-stageinfo-icon breast cancers with a higher Ki-67 index are more likely to return after treatment is completed. These cancers are considered “high risk.” The FDAinfo-icon approved the use of a test to measure this protein in tumors, called the Ki-67 IHC MIB-1 pharmDx test, to determine whether abemaciclib is indicated for use. The FDA guideline says abemaciclib may be an option for people whose Ki-67 index is 20 or higher.

When used, abemaciclib is given with tamoxifeninfo-icon or an aromatase inhibitorinfo-icon (anastrozoleinfo-icon or exemestaneinfo-icon) after the primary treatmentinfo-icon (often surgeryinfo-icon).

“The use of abemaciclib in the early-stage setting depends on reviewing a number of clinicalinfo-icon features to determine if a particular patient is high risk for recurrence, and balancing the potential benefit with possible side effects,” says Tiffany Avery, MD, MPH. “When deciding on the combination with tamoxifen or aromatase inhibitor in a premenopausalinfo-icon patient, the side effectinfo-icon profile of the two should be considered. A premenopausal patient could be treated with agents to induce menopauseinfo-icon in combination with aromatase inhibitor or with tamoxifen alone. Data for other studies suggest that outcomes may be better with induction of menopause in higher risk patients.”

Abemaciclib in metastaticinfo-icon breast cancer

Abemaciclib is FDA approved for three uses in people with hormone receptorinfo-icon-positive, HER2-negative metastatic breast cancer:

  • It is given with an aromatase inhibitor as the first treatment for metastatic breast cancer if you are a postmenopausalinfo-icon woman.
  • It is given alone if you have already been treated with hormonal therapyinfo-icon and chemotherapyinfo-icon for metastatic breast cancer.
  • It is given with fulvestrantinfo-icon (Faslodexinfo-icon) if you have taken hormonal therapy for early-stage or metastatic breast cancer, but have not had chemotherapy since being diagnosed with metastatic breast cancer.

How abemaciclib is given

Abemaciclib is a pill, usually taken twice a day. The recommended doseinfo-icon depends on whether you are taking it alone, with an aromatase inhibitorinfo-icon, with tamoxifeninfo-icon, or with fulvestrantinfo-icon.

Unlike other CDK 4/6 inhibitors, which are taken in cycles with regular breaks, abemaciclib is taken every day through treatment. People with early-stageinfo-icon disease can take abemaciclib for two years. They may stop taking it sooner if the cancer comes back or the side effects are too severe. When given for metastaticinfo-icon breast cancer, abemaciclib may be taken on an ongoing basis for as long as it controls the cancer and side effects are manageable.

Side effects and things to remember

The most common side effectinfo-icon for abemaciclib is diarrheainfo-icon. In a clinical trialinfo-icon, more than 80 percent of participants had diarrhea, but most cases were controlled with anti-diarrheal medicines and lowering the doseinfo-icon, if necessary. Let your doctor know right away if you notice loose stools.

Abemaciclib also may cause neutropeniainfo-icon, a low white blood cellinfo-icon count that makes infectioninfo-icon more likely. Your doctor will watch your blood counts closely, especially during the first two months on the treatment. Other side effects reported in clinicalinfo-icon trials of this medication included:

  • low red blood cell countinfo-icon, which can lead to fatigueinfo-icon
  • low blood platelet count, which can cause abnormalinfo-icon bleeding
  • nauseainfo-icon and vomiting
  • abdominal pain
  • small sores or ulcers in the mouth or on the lips
  • fatigue
  • headache
  • low appetite
  • hair loss
  • itching
  • swelling in the limbs

Tell your doctor about any medicines, supplements, or remedies you are taking before starting abemaciclib. Avoid eating grapefruit and any food or drinks that have grapefruit in them while taking this medicineinfo-icon.

Tell your doctor if you are pregnant, breastfeeding, or planning to do either. Abemaciclib may be dangerous to a fetus so it is recommended that you not take this medicine while pregnant and not get pregnant until at least 3 weeks after you have stopped treatment. It is not known if abemaciclib is transferred through breast milk. For this reason, do not breastfeed while taking abemaciclib or for 3 weeks after you stop.

Talk to your doctor about any side effects you experience and how to manage them. You can also visit our Side Effects page to learn more.

Updated 
July 25, 2022