How does abemaciclib work, and who is it for?

Abemaciclib, sold under the brand name Verzenio (Verzenios in some countries), is a tablet that belongs to a group of medicines called CDK4/6 inhibitors. Every cell that divides has to pass through a series of checkpoints known as the cell cycle. Two proteins, CDK4 and CDK6, act like a key that unlocks the move from the resting stage of the cycle into the stage where the cell copies its DNA and prepares to split. In hormone receptor positive breast cancer, oestrogen pushes the cancer cell to make more of a partner protein called cyclin D, which switches CDK4 and CDK6 on and keeps the cell dividing. Abemaciclib blocks CDK4 and CDK6, so the cancer cell stays stuck at that checkpoint and cannot keep multiplying. Because hormone therapy lowers the oestrogen signal and abemaciclib blocks the step that oestrogen drives, the two work well together, and abemaciclib is almost always given alongside hormone therapy. It is used for breast cancer that is hormone receptor positive and HER2-negative. In early breast cancer it is offered after surgery to people whose cancer has a higher chance of coming back, usually because several lymph nodes were involved. In advanced or metastatic breast cancer it is used to keep the cancer under control for longer. It is not used for HER2-positive or triple-negative breast cancer outside clinical trials.

A signal blocker, not chemotherapy

Abemaciclib targets one growth step inside cancer cells. It is not chemotherapy, and most people do not lose their hair on it, although its side effects still need careful watching.

It needs hormone receptors

The medicine only makes sense when the cancer is driven by oestrogen or progesterone. Your pathology report shows whether your cancer is hormone receptor positive and HER2-negative.

Taken every day without a break

Unlike some other medicines in the same group, abemaciclib is taken twice a day, every day, with no week off.

Abemaciclib is an important medicine, but it helps in specific ways, and it is fair to be clear about them before you start.

It adds to hormone therapy

In large studies, adding abemaciclib to hormone therapy kept cancer from coming back or growing for longer than hormone therapy alone. It does not replace hormone therapy, which usually continues for years after abemaciclib stops.

In advanced disease, it controls rather than removes

For cancer that has spread, the aim is long-term control, often for a good stretch of time, with a good quality of life. It does not make metastatic cancer disappear for good.

Not everyone with early cancer needs it

For people with a low risk of recurrence, the extra benefit is small and the side effects may outweigh it. That is why it is kept for higher-risk early disease.

What this page cannot tell you

It cannot tell you your own risk or whether the benefit outweighs the side effects for you. Your oncologist can weigh your pathology report, scans and health.

Three CDK4/6 inhibitors are widely used in breast cancer: palbociclib, ribociclib and abemaciclib. They share the same basic action but are not identical.

More focus on CDK4

Abemaciclib acts more strongly on CDK4 than on CDK6. Bone marrow cells depend more on CDK6, which may explain why abemaciclib tends to lower blood counts less than the other two. It affects the gut more, so loose motions are its best-known side effect.

A continuous schedule

Because blood counts usually drop less, abemaciclib is taken every day without the planned week off that ribociclib and palbociclib need.

Heart rhythm

Abemaciclib is not known to cause the heart rhythm change that ribociclib can, so routine heart tracings are not usually needed for this reason, though your doctor may still check.

Early breast cancer approval

Abemaciclib was among the first CDK4/6 inhibitors shown to lower the chance of early, node-positive breast cancer coming back after surgery.