Ribociclib (Kisqali) is a targeted therapy approved by the Food and Drug Administration to treat hormone receptor-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 tumor cells reproduce. Those kinases are CDK 4 and CDK 6.

Ribociclib was approved by the FDA in 2017 to treat hormone receptor-positive, HER2-negative advanced or metastatic breast cancer. Two others, palbociclib (Ibrance) and abemaciclib (Verzenio), were approved in 2015 and 2017, respectively. These three medicines mostly work in the same way, although dosing schedules and side effects can vary.

Ribociclib is approved as initial treatment for pre- or perimenopausal women, based on the results of a phase III clinical trial called MONALEESA-7. It also can be used in postmenopausal women and in men. Like the other CDK 4/6 inhibitors, it is given in combination with hormonal therapy, such as an aromatase inhibitor or fulvestrant (Faslodex). In clinical trials, all three medicines have been shown to help people live longer without cancer growth—for several months to a year longer versus hormonal therapy alone.

If you are eligible for a CDK 4/6 inhibitor, your doctor can help you decide between ribociclib and the other medicines.


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 in people with advanced or metastatic, hormone receptor-positive, HER2-negative breast cancer. It can be given with:

  • An aromatase inhibitor as initial treatment in women, regardless of their menopausal status, as well as men
  • Fulvestrant, a selective estrogen receptor downregulator (SERD), also known as an estrogen receptor antagonist (ERA), as initial treatment or after the cancer has grown while being treated with hormonal therapy in postmenopausal women or in men

Pre- or perimenopausal women taking ribociclib plus an aromatase inhibitor need to take an LHRH agonist with it. LHRH agonists suppress hormone production in the body.

Men taking ribociclib plus an aromatase inhibitor or fulvestrant also need to take an LHRH agonist.

Ribociclib’s approval was based on a number of clinical trials:

  • MONALEESA-2: Compared ribociclib plus letrozole in postmenopausal women against letrozole alone
  • MONALEESA-7: Compared ribociclib plus an aromatase inhibitor or tamoxifen (plus the LHRH agonist goserelin) in pre- and perimenopausal women, versus hormonal therapy alone
  • MONALEESA-3: Compared ribociclib plus fulvestrant in postmenopausal women against fulvestrant alone
  • COMPLEEMENT-1: Compared ribociclib plus letrozole against letrozole alone in postmenopausal women, premenopausal women, and men. The latter two groups also received goserelin or leuprolide (both LHRH agonists)

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. Usually, ribociclib can be taken on an ongoing basis for as long as it controls the cancer and side effects are manageable.

Ribociclib can be paired with any aromatase inhibitor. 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. You can also get each medication separately.

Ribociclib can also be given with fulvestrant, which is given as an injection into the buttock. 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 & things to remember

As with any medicine, side effects vary from person to person, but the most common side effects of ribociclib can include:

  • Neutropenia (decrease in white blood cells known as neutrophils), which increases risk of infection
  • Leukopenia (decrease in white blood cells overall), which also increases infection risk
  • Abnormal liver function tests

Your doctor will watch your blood counts, especially during the first two months on the treatment, and perform liver function tests. Your doctor may need to lower the dose or give you a break from treatment if blood tests indicate there is a problem. You can protect yourself from infection by avoiding crowded places and people who are sick, wearing a mask, and washing your hands frequently.

Other side effects that some people may experience include:

Ribociclib also has some rare but potentially serious side effects that you should be aware of. These can include:

  • Inflammation of the lungs
  • Severe skin reaction
  • A heart rhythm problem known as QT prolongation
  • Liver problems

Because of these side effects, your doctor will run tests on your heart and liver function before and during treatment with ribociclib.

Call your doctor right away if you have symptoms such as an irregular heartbeat, chest pain, shortness of breath or difficulty breathing, skin rash, or fatigue. Also be sure to report any signs of infection, such as fever or chills. Getting help right away can prevent a side effect from getting worse.

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 liver disease or heart problems. You should avoid grapefruit and grapefruit juice while you are taking this medicine.

You should avoid becoming pregnant while you are receiving ribociclib and for at least 2 weeks after taking the last dose. Tell your doctor right away if you become pregnant or may be pregnant while you are undergoing treatment.

If you’re a man, ribociclib may affect your fertility (ability to have a child). Talk to your doctor if this is a concern for you.

Your doctor, pharmacist, or nurse can help you manage your side effects. If you experience difficult side effects, your doctor may recommend lowering the dose or stopping the medication temporarily. You can go to our section on Side effects for more information.


Related resources


Reviewed and updated: April 21, 2023

Reviewed by: Sameer Gupta, MD, MPH


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