What Are CDK4/6 Inhibitors?

cancer-cells-3D-render-cancer-cells-inhibitors | Feature | What Are CDK4/6 Inhibitors?

CDK 4/6 inhibitors are a class of medication used to treat some types of breast cancer. Here’s a closer look at these targeted therapies.

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In this article:

  1. What Are CDK4/6 Inhibitors?
  2. Types of CDK4/6 Inhibitors
  3. What Are The Side Effects of CDK4/6 Inhibitors?
  4. Taking CDK4/6 Inhibitors

What Are CDK4/6 Inhibitors?

cancer-cells-3D-render | What Are CDK4/6 Inhibitors? | What Are CDK4/6 Inhibitors?

Cyclin-dependent kinase (CDK) 4/6 inhibitors are a newer class of medicines that interrupt the cell division process in some metastatic breast cancer. More specifically, it targets cyclin-dependent kinases 4 and 6 proteins.

CDK4/6 inhibitors may treat women and men once cancer progresses after hormonal therapy treatment and earlier chemotherapy for metastatic breast cancer. In selected cases, doctors may also use CDK4/6 inhibitors to treat advanced breast cancer.

Both healthy cells and cancer cells have CDK4/6 proteins that control how fast they grow and divide. When these proteins become overactive, like in metastatic breast cancer, cells divide and grow unrestrained. CDK4/6 inhibitors work by impeding these proteins. As a result, cell division slows down, or cancer cells stop growing.

These inhibitors manage metastatic, hormone receptor-positive (HR+), human epidermal growth factor receptor 2-unamplified (HER2-) breast cancer. Estrogen, progesterone, or both fuels HR+ cancer, whereas epidermal growth factor receptor 2 promotes cancer cell growth.

The majority of breast cancers are HR+ and HER2-. For this reason, treatments that target the HER2 protein, for example, Herceptin, aren’t suitable for HER2- cancers.

Types of CDK4/6 Inhibitors

The current CDK4/6 inhibitors used in breast cancer treatment include:

  • Palbociclib (Brand name: Ibrance)
  • Ribociclib (Brand name: Kisqali)
  • Abemaciclib (Brand name: Verzenio)

While all three are pills taken orally, the way to use them differs somewhat.

Ibrance and Kisqali work alongside hormonal therapy and affect both CDK4 and CDK6. Treatment consists of 4-week cycles that include a week-long break. It also includes medicine to suppress ovarian function for premenopausal and perimenopausal women.

On the other hand, patients take Verzenio daily, alone or in conjunction with other therapies. Additionally, it seems to influence the CDK4 protein more than the CDK6 protein.

Doctors consider all three equally effective, but some factors may determine the right option for each case, such as:

  • If the patient is premenopausal or postmenopausal
  • Previous treatments
  • Cancer progression
  • Preferred treatment schedule 4-week cycles or daily)
  • Side effects
  • Which option the patient’s health insurance favors

All three medications are FDA approved for use in different subgroups. But approvals are likely to change as ongoing trials find benefits for other groups.

Pregnant women or those planning to get pregnant shouldn’t take CDK4/6 inhibitors as they can harm the fetus. Therefore, patients should use effective birth control for three weeks after the final dose. Men should also use contraception at least three months after finishing treatment.

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What Are The Side Effects of CDK4/6 Inhibitors?

Side effects may be more pronounced with CDK4/6 inhibitors than others. But they also tend to be less severe than those caused by chemotherapy and most often include:

  • Nausea
  • Fatigue
  • Diarrhea
  • Anemia (low red blood cell counts)
  • Low platelet counts
  • Neutropenia (low white blood cell counts)

These medications may also affect the liver, and doctors may order liver function tests while the patient adjusts to treatment.

Side effects may also influence treatment. For instance, Verzeno has a significant risk of gastrointestinal (GI) issues. Most patients can manage side effects with anti-diarrhea medicine or diet. In some cases, a patient may do better on a lower dose or by taking a break from treatment for a month or more. However, in roughly 10% of patients, severe diarrhea may lead to dehydration or infection. If a patient has a history of GI issues like colitis or irritable bowel syndrome, doctors may favor the other inhibitors.

In rare cases, Kisqali can cause a fast or irregular heartbeat, known as QT interval prolongation, which may be life-threatening.

Notably, this is not an exhaustive list, and side effects can vary widely from person to person.

Taking CDK4/6 Inhibitors

Starting any treatment comes with challenges, but some planning can help make the transition smoother.

Firstly, know potential side effects, whether any other medications you’re taking might interact with the CDK4/6 inhibitor, the time of the day to take the pill(s), and what to do if you miss a dose.

Additionally, investigate out-of-pocket costs. Treatment can be costly, but in some cases, patients qualify for financial assistance.

Since treatment often includes hormonal therapy, it may be beneficial to create a system for organizing medication. A pill organizer and a smartphone or watch reminder may help patients stay on track with their medication schedule.

Specialty pharmacies often mail CDK4/6 inhibitors to a patient’s home. Therefore, it’s vital to ensure coordination between doctors, patients, and pharmacies to avoid treatment delays.

Initially, dose adjustments are typical, and it’s essential to prepare for frequent blood and liver function tests.

During the first weeks of treatment, side effects are usually at their worst. Patients should plan their schedules accordingly and may need to reduce activity levels. A plan to manage and prevent diarrhea is helpful, as well. Infections are also more common during treatment. Patients should wash their hands frequently, avoid sick people and crowds.

In short, CDK4/6 inhibitors are a class of drugs that target CDK4 and CDK6 proteins and hinder the growth of cancer cells. The three types are Palbociclib (Ibrance), Ribociclib (Kisqali), and Abemaciclib (Verzenio). These drugs are used in combination with hormone therapy to treat some metastatic breast cancers. Lastly, side effects do occur but to a lesser extent than with chemotherapy.
If you’re interested in learning more about epigenetics and research developments, visit the TruDiagnostic website today. 

Are you taking CDK4/6 inhibitors? We want to hear about your experience! Share your thoughts in the comment section below.


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