The European Commission granted a marketing authorisation valid throughout the European Union for Ibrance on 9 November 2016. Ibrance contains the active substance palbociclib and is a cancer medicine used to treat locally advanced or metastatic breast cancer but can only be used when the cancer cells are HR-positive and HER [human epidermal growth factor] negative. It has been approved because it has been shown to prolong the time patients live without their disease getting worse by an average of 6 to 10 months, which is considered of clear clinical value. The active substance blocks the activity of cyclin-dependent kinases (CDK) 4 and 6, which play a key role in regulating the way cells grow and divide. In some cancers, including HR-positive breast cancer, the activity of CDK 4 and 6 is increased, which helps the cancer cells to multiply uncontrollably. By blocking CDK4 and CDK6, palbociclib slows the growth of HRpositive breast cancer cells. Palbociclib has been studied in two main studies of women with HR-positive, HER2-negative breast cancer. In both studies, the main measure of effectiveness was how long patients lived without their disease getting worse (progression-free survival). The first study involved 521 women with metastatic breast cancer that had got worse after treatment with a hormonal medicine. They received either I palbociclib and fulvestrant or a placebo and fulvestrant. Women taking palbociclib and fulvestrant lived on average 11.2 months without their disease getting worse compared with 4.6 months for women taking placebo and fulvestrant. The second study involved 666 women who had been through the menopause and whose breast cancer had started to spread and who had not yet received cancer treatment. They received either palbociclib and letrozole (an aromatase inhibitor) or placebo and letrozole. Women taking palbociclib and letrozole lived on average 24.8 months without their disease getting worse compared with 14.5 months for women taking placebo and letrozole. The most common side effects with palbociclib are neutropenia, infections, leucopenia, tiredness, nausea, stomatitis, anaemia, alopecia and diarrhoea. The most common severe side effects with Ibrance are neutropenia, leucopenia, anaemia, tiredness and infections.