New CDK4/6 Inhibitor Gets FDA Breakthrough Therapy Designation

Ribociclib (LEE011) shows promise as first line of treatment for postmenopausal women with metastatic breast cancer that is hormone receptor-positive and HER2-negative
Breast Cancer News
September 2, 2016
Erin Rowley, Writer and Content Coordinator
Reviewed By: 
Kathy D. Miller, MD

In August, the pharmaceutical company Novartis announced that its medicineinfo-icon ribociclib (LEE011) was granted a special status, breakthrough therapyinfo-icon designation, by the U.S. Food and Drug Administrationinfo-icon (FDAinfo-icon). This status helps medicines under study move through the FDA review process more quickly.


Ribociclib is a type of medicine called a cyclin-dependent kinase (CDK) 4/6 inhibitor. Cyclin-dependent kinases 4 and 6 are two proteins that cause tumorinfo-icon cells in some breast cancers to grow. CDK 4/6 inhibitors like ribociclib work by blocking CDK 4 and 6 from telling cancer cells to multiply. This can slow the growth or spread of cancer cells.

CDK 4/6 inhibitors are a fairly new class of medicines. Only one, palbociclib (Ibrance), is currently FDA-approved, for use in metastaticinfo-icon hormone receptorinfo-icon-positive breast cancer with a type of hormonal therapyinfo-icon called an aromatase inhibitorinfo-icon. Palbociclib also received breakthrough therapy designation before it was approved by the FDA.

Breakthrough Therapy Designation

The FDA has granted breakthrough therapy designation to medicines since 2013. Medicines can get this designation if they are intended to treat a serious illness and if early clinicalinfo-icon trials suggest the medicine works considerably better than existing therapies.

When a medicine gets breakthrough therapy designation, the FDA speeds up its normal review process. This way, if the medicine does get FDA approval, it can be made available to the public as soon as possible. 


Results from the phase III MONALEESA-2 trial are responsible for ribociclib’s breakthrough therapy designation. The trial results haven’t been published or presented yet. But researchers ended the trial early, in May, because the medicine, when given with the aromatase inhibitor letrozoleinfo-icon (Femarainfo-icon), met their goal of significantly improving progression-free survivalinfo-icon (PFS) compared to letrozole alone. PFS is the length of time after receiving the study medicine that the disease is still present but does not get worse. The researchers are still collecting data about overall survival (OS), the time from start of participation in the study to death from any cause.

For more information about the study and the criteria people had to meet to take part in it, see this article LBBC posted about the study in 2014, when researchers were still recruiting participants.

Ongoing Studies

Other studies looking at ribociclib are still ongoing. A study called MONALEESA-3 is looking at ribociclib in combination with another aromatase inhibitor, fulvestrantinfo-icon (Faslodexinfo-icon), versus fulvestrant alone. MONALEESA-3 recruited men and postmenopausalinfo-icon women who have breast cancer that is metastatic, hormone receptor-positive and HER2-negative, and who have had no more than one prior line of treatment for metastatic disease.

A study called MONALEESA-7 is looking at ribociclib in combination with hormonal therapy and goserelininfo-icon (Zoladex) versus hormonal therapy and goserelin alone in premenopausalinfo-icon women with metastatic hormone receptor-positive, HER2-negative breast cancer who haven’t had hormonal therapy before.

What This Means for You

Ribociclib’s breakthrough therapy designation won’t change your treatment options right away. The medicine is still considered experimentalinfo-icon, so for the most part, it’s only available through clinical trials. In certain cases you might be able to get this medicine without joining a trial. Your doctor will be able to tell you whether it's available to you.

But this designation shows that people at the FDA are excited about ribociclib. It also shows that if the medicine proves to be safe, effective, and better than current therapies, they want to make sure it becomes FDA-approved and available to people like you as soon as possible.

You can find more information about targeted therapies for hormone receptor-positive metastatic breast cancer here, and more general info about metastatic breast cancer here.

Additional Related Topics 
Hormone Receptor-Positive
Clinical Trials
Hormonal Therapy
Targeted Therapy