What exactly are CDK4/6 inhibitors, and why are so many of us with ER+/PR+/HER2- breast cancer taking them?
When I was diagnosed with Stage 2B ER+/PR+/HER2- breast cancer, I quickly learned that treatment isn’t just about getting rid of the cancer that’s there. It’s also about lowering the chance that microscopic cancer cells left behind will ever wake up again.
That’s where CDK4/6 inhibitors come in.
Think of every cell as having a “go” signal that tells it when to divide and multiply. Cancer cells hijack that signal.
CDK4 and CDK6 are proteins that act like engines driving the cell cycle forward. CDK4/6 inhibitors block those proteins, essentially putting the brakes on cancer cells so they can’t keep dividing. When combined with hormone therapy, they make it much harder for hormone receptor-positive breast cancer cells to grow and spread.
For years, these medications transformed the treatment of metastatic ER+/HER2- breast cancer, helping many people live longer with better disease control.
Now they’re also changing the outlook for people with high-risk early-stage breast cancer.
Two landmark clinical trials helped make this possible:
• monarchE studied abemaciclib (Verzenio) plus hormone therapy in people with high-risk Stage II and Stage III ER+/HER2- breast cancer. It showed a significant reduction in the risk of the cancer returning compared with hormone therapy alone. (PMC)
• NATALEE studied ribociclib (Kisqali) plus hormone therapy. It included an even broader group of Stage II and Stage III patients and also demonstrated a meaningful reduction in recurrence risk. That’s one of the reasons ribociclib is now an option for many people with high-risk early breast cancer—not just those with metastatic disease. (JAMA Network)
Of course, these medications aren’t easy.
They can cause fatigue, low white blood cell counts, nausea, diarrhea or constipation, liver abnormalities, heart rhythm changes, and other side effects. Every person’s experience is different, and not everyone is a candidate.
That’s why it’s so important to have an honest conversation with your oncology team about the risks and the benefits based on your individual cancer, your recurrence risk, and your overall health.
For me, taking Kisqali is one more layer of protection. It isn’t always fun, and there are days when the side effects remind me I’m still in treatment. But if it helps reduce the chance of recurrence, it’s a trade-off I’m personally willing to make.
Knowledge is power. Ask questions. Understand your options. And remember that every treatment decision should be made together with your medical team.
If you’re taking a CDK4/6 inhibitor like Kisqali or Verzenio, I’d love to hear your experience. How has it been going for you?
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