For patients with metastatic breast cancer, learning that the cancer has spread to other parts of the body may mean daunting treatment regimens of chemotherapy and its difficult side effects. But some patients—those with hormone receptor-positive and HER2-negative metastatic breast cancer—may be able to postpone chemotherapy for breast cancer in some cases for up to a year by taking hormone therapy. Now some of those patients may have an even longer reprieve, putting off chemotherapy treatments for more than two years, thanks to a new class of drugs approved for metastatic breast cancer.
“This is one of the biggest advances we've had in metastatic breast cancer in a long time.” - Sramila Aithal, MD, Hematologist-Oncologist, Medical Oncologist
What are kinase inhibitors?
These new drugs belong to a common class of targeted therapy cancer drugs called kinase inhibitors. A kinase is a protein on a cell that acts like a dispatcher, receiving signals from other cells and then passing on the instructions into its cell's nucleus. Once the signal is delivered, a cell may perform any number of functions, including growing or dividing or even shutting itself off. These specific drugs for breast cancer target two kinase proteins—CDK 4 and CDK 6—that help regulate cell growth and division. Blocking these proteins may help slow cancer cell growth. Some patients with HR-positive and HER-negative metastatic breast cancer have experienced positive outcomes by combining a CDK 4/6 inhibitor with hormone therapy.
"Women used to get hormone treatment alone for their cancer and were able to be free from cancer or have a response for up to a year, maybe 16 months in some cases," says Sramila Aithal, MD, Hematologist-Oncologist, Medical Oncologist and head of the Breast Cancer Center at our hospital in Philadelphia. "But by adding this other therapy that targets the CDK 4/6, they have had better responses for more than two years. More important, many people would have chemotherapy for metastatic cancer, especially if it invaded an organ, like the liver or lung. But by using this treatment combination, they’ve been able to postpone chemotherapy for up to 27 or 28 months. That's made a big difference."
CDK 4/6 inhibitors:
So far, three CDK 4/6 inhibitors have been approved by the U.S. Food and Drug Administration to treat metastatic breast cancer:
- Palbociclib (Ibrance®), approved in 2015
- Ribociclib (Kisqali®), approved in April 2017
- Abemaciclib (Verzenio™), approved in September 2017
Palbociclib and ribociclib are usually given with the anti-estrogen drug fulvestrant (Faslodex®), which regulates hormones. Abemaciclib is the first CDK 4/6 inhibitor approved as a stand-alone therapy. CDK 4/6 inhibitors are approved only for HR-positive and HER-negative breast cancer, but clinical trials are underway to determine whether they may be used to treat other cancers, including lung, prostate and other types of breast cancer. Common side effects of these inhibitors include diarrhea, nausea, and fatigue. "These are oral medications, they are easy to administer, and they are very tolerable," Dr. Aithal says. "It’s a huge shift in the paradigm of the way we treat breast cancer."
