• Both Verzenio and Ibrance belong to the same class of medicine, called CDK 4/6 inhibitors.
• Because they are both in the same class of medicines, clinically, there seems no advantage in switching from one to another if one drug fails.
• However, research has shown breast cancer cells can acquire resistance to CDK 4/6 inhibitors by producing higher amounts of CDK6.
• Laboratory trials showed a “treatment holiday” of 28 days reversed this resistance.
• Because of this, there may be some benefit of either stopping Ibrance temporarily or switching from Ibrance to Verzenio after a treatment break.
• Comparative trials comparing Verzenio to Ibrance are currently underway with results expected in 2023.

Both Verzenio and Ibrance are CDK 4/6 inhibitors, a type of targeted treatment that helps to reduce the growth and spread of cancer cells in the body. The active ingredient in Verzenio is abemaciclib and in Ibrance it is palbociclib.

• Both Verzenio and Ibrance are used to treat advanced or metastatic breast cancer in women with HR-positive, HER2-negative disease. They are given when cancer has progressed or spread to other parts of the body despite other treatments.
• Verzenio can also be used to treat adults with early breast cancer at high risk of recurrence in combination with endocrine treatment (tamoxifen or an aromatase inhibitor). Ibrance is not approved for early breast cancer.
• Both Verzenio and Ibrance can be used in combination with an aromatase inhibitor or, in those who have not reached menopause, with fulvestrant intramuscular injection. Both Verzenio and Ibrance can be used in men.
• Only Verzenio can be used alone (as monotherapy) for adult patients with HR-positive, HER2-negative disease.

Because Verzenio and Ibrance are similar treatments and have not been compared in head-to-head trials, the benefits of switching to Verzenio after Ibrance has failed is unknown.

However, research has shown that breast cancer cells can acquire resistance to CDK 4/6 inhibitors by producing higher amounts of CDK6. This will be shown by tumor growth in imaging studies.

• Laboratory studies suggest this may be reversible by having a treatment holiday of 28 days (4 weeks).
• Upon starting the CDK 4/6 inhibitor again, the tumors shrank.
• In light of this information, a switch from one CDK 4/6 inhibitor to another, with a treatment holiday period in between, could be considered.
• More research is needed, and trials are underway that are comparing the effects of Ibrance and Verzenio with an aromatase inhibitor and other medications in the treatment of breast cancer. Results are likely to be published in 2023.

What is the difference between Verzenio and Ibrance?

There may also be some advantages for Verzenio over Ibrance.

• Verzenio is taken twice daily, every day. Ibrance is taken every day for 21 days followed by a 7-day break.
• Verzenio can be used as monotherapy or in combination with other treatments. Ibrance is always taken in combination with either an aromatase inhibitor or fulvestrant.

There may be some disadvantages too. Verzenio is more likely than Ibrance to cause diarrhea; however, most patients can manage this side effect with the anti-diarrhea medication loperamide.

How do Verzenio and Ibrance work?

Verzenio and Ibrance belong to the class of medicines known as CDK4/6 inhibitors.

CDK4/6 inhibitors target particular enzymes, called CDK4 and CDK6. CDK stands for cyclin-dependent kinase, and it is an enzyme that is important for cell division. CDK4/6 inhibitors interrupt signals that stimulate the growth of cancerous cells.

Certain cancers, for example, hormone-receptor-positive breast cancer, are more likely to have disturbances in CDK4/6, and CDK 4/6 inhibitors may form part of the treatment protocol.

Most often, CDK4/6 inhibitors are given at the same time as hormonal therapy (such as an aromatase inhibitor or fulvestrant), although Verzenio may be used alone to treat hormone receptor-positive, HER2-negative metastatic breast cancer in pre-treated patients.

Research suggests CDK4/6 inhibitors may increase the time people have before cancer spreads. More evidence is needed to determine their impact on overall survival.

Common side effects include fatigue and gastrointestinal disturbances, such as nausea, severe diarrhea, and vomiting. Bone marrow suppression resulting in neutropenia and leukopenia may also occur, although anemia and thrombocytopenia are less common. In general, the side effects associated with CDK4/6 inhibitor therapy are less severe than those experienced with chemotherapy.