What to expect from CDK4/6 inhibitor therapy for hormone receptor-positive breast cancer

CDK4/6 inhibitors block proteins that help cancer cells divide. For hormone receptor-positive breast cancer, they are commonly used with endocrine therapy; the exact combination depends on whether treatment is for disease in the breast, after surgery, or for cancer that has spread. Your prescription will specify the medicine, dose, cycle pattern, and whether tablets are taken continuously or with planned breaks.

The team checks blood counts and liver tests, and may review heart rhythm or other medicines depending on the drug. Possible effects include tiredness, nausea, diarrhoea or constipation, reduced appetite, mouth soreness, hair thinning, and low white blood cells. Some medicines have distinctive risks, so use the product-specific instructions you receive.

Take each dose exactly as prescribed and use a calendar or phone reminder. If you miss a dose or vomit after taking one, call the oncology team for instructions rather than doubling the next dose. Tell them about all medicines, vitamins, and herbal products because interactions can alter drug levels. Report infection symptoms, drink fluids if advised, and keep scheduled blood tests even when you feel well.

Do not stop endocrine therapy or the inhibitor on your own. The team may pause treatment or adjust the dose to manage side effects while preserving the treatment plan.

Contact your oncology team promptly for fever, chills, a new cough, painful urination, severe diarrhoea, yellowing of the skin or eyes, unusual bleeding, marked breathlessness, chest pain, or a fast or irregular heartbeat. Seek emergency care for severe breathing difficulty, fainting, or sudden chest pressure.

Ask how to take your specific inhibitor, which foods or medicines to avoid, when blood tests are due, what counts as a missed dose, how side effects will be treated, and how this medicine fits with surgery, radiotherapy, or endocrine therapy.