Abemaciclib (Verzenio) is a targeted therapy approved by the Food and Drug Administration to treat hormone receptor-positive metastatic 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 tumor cells reproduce. Those kinases are CDK 4 and CDK 6.
CDK 4/6 inhibitors are relatively new treatments. The first, palbociclib, was approved by the FDA in 2015. Another, ribociclib, was approved in early 2017. Abemaciclib is the third medicine of this type to be approved for hormone receptor-positive, HER2-negative metastatic breast cancer.
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 telling cancer cells to multiply, which helps slow the growth or spread of the cancer.
- It is given with an aromatase inhibitor as the first treatment for metastatic breast cancer if you are a postmenopausal woman.
- It is given alone if you have already been treated with hormonal therapy and chemotherapy for metastatic breast cancer.
- It is given with fulvestrant (Faslodex) 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.
The most common side effect for abemaciclib is diarrhea. In a clinical trial, more than 80 percent of women experienced diarrhea, but most cases were controlled with anti-diarrheal medicines and lowering the dose, if necessary. It also may cause neutropenia, a low white blood cell count that makes infection more likely. Your doctor will watch your blood counts closely, especially during the first two months on the treatment. Other side effects included:
- low red blood cell count, which can lead to fatigue
- low blood platelet count, which can cause abnormal bleeding
- nausea and vomiting
- abdominal pain
- small sores or ulcers in the mouth or on the lips
- low appetite
- hair loss
- swelling in the limbs
Tell your doctor about any medicines, supplements or remedies you are taking before starting abemaciclib. You should avoid eating grapefruit and any food or drinks that have grapefruit in them while taking this medicine.
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, so you should also 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.