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What Are CDK4/6 Inhibitors?
CDK4/6 inhibitors are a class of medicines used to treat certain types of metastatic breast cancer, which is cancer that has spread to other parts of the body, such as the bones or liver.
CDK4/6 inhibitors are a newer class of medicines used to treat certain types of metastatic breast cancer, which is cancer that has spread to other parts of the body, such as the bones or liver. These medicines interrupt the process through which breast cancer cells divide and multiply. To do this, they target specific proteins known as the cyclin-dependent kinases 4 and 6, abbreviated as CDK4/6. That's why you may hear them referred to as “targeted therapies.” If a breast cancer is hormone-receptor-positive, it means the cancer’s growth is fueled by the hormones estrogen, progesterone, or both. HER2-negative cancers have tested negative for a protein called human epidermal growth factor receptor 2, or HER2, which promotes cancer cell growth. So HER2-negative cancers don’t respond to treatments that target the HER2 protein (such as Herceptin). More than two out of every three breast cancers are both hormone-receptor-positive and HER2-negative. 1 Currently there are three CDK4/6 inhibitors used to treat metastatic breast cancer:
The CDK4/6 proteins, found both in healthy cells and cancer cells, control how quickly cells grow and divide. In metastatic breast cancer, these proteins can become overactive and cause the cells to grow and divide uncontrollably. CDK4/6 inhibitors interrupt these proteins in order to slow or even stop the cancer cells from growing. All three CDK4/6 inhibitors are pills taken by mouth, but they are used a little bit differently. Verzenio is a pill that you take every day, either alone or with other treatments. It appears to affect the CDK4 protein more than the CDK6 protein. Ibrance and Kisqali affect both CDK4 and CDK6 and have to be taken along with hormonal therapy. They are also given in 4-week cycles that include a week-long break — so you would take the medication for 3 weeks and then take 1 week off.
Ibrance, Kisqali, and Verzenio have not been directly compared to each other in a clinical trial. Still, doctors consider them to work equally well. Your treatment team can help you decide which one is right for your situation. This may depend on factors such as: the stage of the breast cancer what treatments you have had in the past, if any how quickly the cancer progressed after previous treatment if you are a woman, whether you are premenopausal or postmenopausal the side effects associated with each CDK4/6 inhibitor whether you and/or your treatment team prefer that you take medication continuously, as you would with Verzenio, or on a 3-week on/1-week off cycle (Ibrance and Kisqali) whether your health insurance favors one of the medications over the others Each CDK4/6 inhibitor is approved by the U.S. Food and Drug Administration (FDA) to treat certain stages of hormone-receptor-positive HER2-negative breast cancer in different groups of people. (If you live outside the United States, not all of these CDK4/6 inhibitors may have been approved yet, so check with your doctor.) Keep in mind that these approvals are likely to change over time, as clinical trials are still ongoing to figure out if CDK4/6 inhibitors can benefit additional groups. All the CDK4/6 inhibitors are approved to treat advanced-stage and metastatic hormone-receptor-positive, HER2-negative breast cancer. Advanced-stage breast cancer is cancer that has come back (recurred) or spread beyond the breast to the chest wall below the breast. Metastatic breast cancer is advanced-stage cancer that has spread to parts of the body away from the breast, such as the bones or liver.
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