Low white cell counts on ribociclib: expected and managed

A fall in white blood cells is the most common side effect of ribociclib, sold as Kisqali. Ribociclib blocks proteins called CDK4 and CDK6, which cancer cells use to divide. The bone marrow also relies on these proteins to make new white cells, so while you take the tablets, production of neutrophils slows down. Neutrophils are the white cells that fight bacterial infection. In trials, most people had some drop in their neutrophil count, and many had a drop large enough to need a delay, pause or lower dose. The good news is that this effect is different from chemotherapy. Ribociclib mainly slows the marrow rather than damaging it, so counts usually recover during the week off or after a short break, and serious infections with a fever are uncommon. The count tends to be lowest towards the end of the three weeks on tablets. This is why blood counts are checked every two weeks during the first two cycles, then at the start of later cycles. If your count is too low, your doctor will usually delay the next cycle by a few days, or restart at a lower dose. Analyses of trial data suggest that people who needed a lower dose still seemed to benefit. Growth factor injections to boost white cells are not usually needed. The most important thing you can do is report a fever or signs of infection straight away.

Very common, usually manageable

Most people have a lower count at some point, and most carry on with treatment.

Counts recover

The week off and short pauses give the marrow time to catch up.

Fever needs urgent advice

A temperature or feeling shivery and unwell should never be left until the next day.

Low counts on ribociclib are usually manageable, but that does not make infections harmless.

Serious infections can happen

They are uncommon, but when they happen they can become serious quickly. Speed of treatment makes a real difference.

Delays can be frustrating

Repeated delays and dose changes can feel like setbacks, even though they are a normal part of safe treatment.

Some people have lower counts to start with

Some people naturally have lower neutrophil counts, and some studies suggest people of Asian background may have more count drops on ribociclib. Your team will take this into account.

What this page cannot tell you

It cannot interpret your own count or tell you when to restart. Your team uses your results and health to decide.

You do not usually need to stay at home or isolate. Simple precautions lower the risk of infection.

Hand washing

Wash hands before eating, after using the toilet and after being in public places.

Food safety

Eat freshly cooked food, wash fruit and vegetables well, and avoid street food and undercooked meat or eggs when counts are low.

Crowds and illness

Avoid close contact with people who have a cough, cold or fever, and consider very crowded places carefully when your count is at its lowest.

Vaccines

Ask your team about the flu and other inactivated vaccines. Live vaccines are usually avoided.