CDK 4/6 Inhibitors Are Important Tools

Are you or a loved one facing complex treatment decisions because of hormone receptor-positive metastatic breast cancer? LBBC, Medscape Education/WebMD Education and SHARE recently partnered to develop an interactive online tool, “I Have Metastatic Breast Cancer: What Are My Options?” Through this step-by-step educational resource, people with metastatic hormone receptor-positive breast cancer and their caregivers can become more comfortable and confident in making decisions that impact their treatment.

Evelyn Robles-Rodriguez, RN, MSN, APN, AOCN, is the director of outreach, prevention and survivorship at MD Anderson Cancer Center at Cooper. She frequently reviews LBBC content and takes part in LBBC programs, and worked on the online tool. Here, Ms. Robles-Rodriguez tells us more about one of the classes of medicines the tool addresses: CDK 4/6 inhibitors.

As our quest to treat breast cancer continues, three relatively new medicines called CDK 4/6 inhibitors have been added as tools to treat hormone receptor-positive (HR+), HER2-negative (HER2-) metastatic (advanced) breast cancer. These medicines, also known as cyclin-dependent kinase inhibitors, target the function of the CDK cells, thus suppressing cancer cell division and growth.

More importantly, the use of these medicines can help extend the time that the patient does not have progression of the disease, as well as help patients maintain quality of life while on chronic treatment of the disease.

The three innovative medicines are:

• Palbociclib (Ibrance). It was approved for treatment with letrozole (Femara) in February 2015 and showed a progression-free survival of 26.1 months. This medicine can be used along with an aromatase inhibitor as initial therapy for postmenopausal women with metastatic breast cancer that is hormone receptor-positive, HER2-negative, as well as a second-line therapy in combination with fulvestrant (Faslodex) for women of any menopausal status whose cancer progressed while on hormonal therapy.
• Ribociclib (Kisqali). It was approved by the FDA in March 2017 in combination with letrozole and showed a progression-free survival of 25.3 months. This medicine can be used with an aromatase inhibitor as initial therapy for postmenopausal women with metastatic breast cancer that is hormone receptor-positive, HER2-negative.
• Abemaciclib (Verzenio). It was approved in September 2017, with progression-free survival similar to the two medicines above. This medicine can be used alone in women or men with hormone receptor-positive, HER2-negative metastatic breast cancer, whose cancer progressed while on hormonal therapy and chemotherapy; with fulvestrant for women of any menopausal status whose cancer progressed while on hormonal therapy; or with an aromatase inhibitor as initial therapy for postmenopausal women.

People taking CDK 4/6 inhibitors generally tolerate the side effects quite well, although there can be differences in side effects between the three medicines. More common side effects include decreased white blood cells and fatigue. Abemaciclib can also cause bothersome diarrhea. There are other potential side effects which are monitored closely by the health care team. Doses can be modified to help improve symptoms. Remember not to eat grapefruits or drink grapefruit juice while taking these medicines, since grapefruits can affect how well they work. If you are taking a CYP3A medicine, please let your doctor know as those medicines can interact with the CDK 4/6/ inhibitors. Common CYP3A medicines include ketoconazole (Nizoral), midazolam (Versed), rifampicin (Rifadin) and phenytoin (Dilantin). Also, it is important to use effective contraception as all three medicines can cause fetal harm.

To find out more about the use of these exciting and important medicines in breast cancer treatment, consider looking at “I Have Metastatic Breast Cancer: What Are My Options?” This interactive tool will educate you about the treatment of metastatic breast cancer, including the use of CDK4/6 inhibitors, as well as provide you with tips for working with your healthcare team.