Ribociclib (Kisqali), a targeted therapy, is the second CDK 4/6 inhibitor to be approved by the FDA. It targets two specific kinases, or enzymes, that help tumor cells grow and divide.

How ribociclib works

Cyclin-dependent kinase 4 and 6 are two enzymes that help tumor cells grow and multiply. By blocking the action of CDK 4 and 6, ribociclib interferes with signals that tell cancer cells to quickly reproduce. This helps slow or even stop the growth or spread of cancer cells.

Who gets ribociclib

Ribociclib is approved for use with an aromatase inhibitor as initial or first-line treatment for women with metastatic, hormone receptor-positive, HER2-negative breast cancer.

It is also approved with fulvestrant (Faslodex), a type of hormonal therapy, for postmenopausal women with metastatic, hormone receptor-positive, HER2-negative breast cancer. Postmenopausal women have permanently stopped getting their monthly periods because of age or cancer treatment. The combination of ribociclib and fulvestrant may be given as initial treatment or after the cancer has grown while being treated with a different hormonal therapy.

How ribociclib is given

Ribociclib is a pill. It is usually taken once a day for the first 21 days of a 28-day cycle. The pill can be taken with or without food, and should be taken at the same time each day, preferably in the morning.

It may be given with an aromatase inhibitor, which is also a pill. The aromatase inhibitor should also be taken once a day, at the same time each day, preferably in the morning. It is taken for all 28 days of the cycle.

You and your doctor will discuss how many times you should repeat this cycle.

Ribociclib can be paired with any aromatase inhibitor. But if your doctor recommends letrozole (Femara), a 28-day supply of the medicines can be sold together. This is called a Kisqali Femara Co-Pack. It requires one copay rather than two, and costs the same as ribociclib alone, according to Novartis, the company that makes both medicines.

Ribociclib can also be given with fulvestrant, which is given as a shot to the buttocks. In the first month fulvestrant is given as two shots every 2 weeks, after that it is given as two shots every 4 weeks.

Side effects and things to remember

The most common side effects of riboclicib are listed below.

About 50 percent of people who take ribociclib experience nausea.

Between 30 and 40 percent of people who take ribociclib have the following side effects:

Between 20 and 30 percent of people who take ribociclib have the following side effects:

  • Vomiting
  • Constipation
  • Headache
  • Back pain

Three out of four people who take ribociclib experience neutropenia and one out of three experience leukopenia, low white blood cell counts. These side effects, when caused by chemotherapy, often increases risk of infection. When caused by ribociclib, that does not appear to happen.

An irregular heartbeat is an uncommon but serious possible side effect of ribociclib. Your doctor will run tests on your heart before and during treatment with ribociclib.

These are not all the possible side effects of ribociclib. More can be found here.

Before starting ribociclib, be sure to tell your doctor about any medicines you are taking, including vitamins, herbal supplements and over the counter medicines. Also tell your doctor if you have ever had heart or liver problems. You should avoid grapefruit and pomegranate, as well as their juices, while you are taking this medicine.

You should avoid becoming pregnant, and breastfeeding, while you are taking ribociclib and for at least 3 weeks after taking the last dose. Tell your doctor right away if you become pregnant or may be pregnant while you are undergoing treatment.

Your doctor, pharmacist or nurse can help you manage your side effects. You can also go to our section on Side Effects for more information.



Reviewed and updated: June 25, 2019

Reviewed by: Heather McArthur MD, MPH


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Living Beyond Breast Cancer is a national nonprofit organization that seeks to create a world that understands there is more than one way to have breast cancer. To fulfill its mission of providing trusted information and a community of support to those impacted by the disease, Living Beyond Breast Cancer offers on-demand emotional, practical, and evidence-based content. For over 30 years, the organization has remained committed to creating a culture of acceptance — where sharing the diversity of the lived experience of breast cancer fosters self-advocacy and hope. For more information, learn more about our programs and services.