[Inhibitors of cyclin-dependent kinases (CDK) - a new group of medicines in therapy of advanced breast cancer].

Cyclin-dependent kinases (CDKs) are a family of enzyme proteins present in cell nuclei that regulate the various stages of the cell cycle. They act as proto-oncogens, and increased expression of some of these proteins (CDK4 and CDK6) is observed in breast cancer cells and associated with decreased sensitivity to anti-estrogen therapy. CDK inhibitors are chemicals that inhibit the enzymatic activity of specific CDKs. Currently three drugs in this group are available on the market and are registered for the treatment of advanced HR-positive, HER2-negative breast cancer. Two drugs in this class (palbociclib and ribociclib) are registered for first-line treatment in combination with letrozole, two (palbociclib and abemaciclib) are approved for second line therapy in combination with fulvestrant. In both indications, the addition of a CDK inhibitor to standard hormone therapy doubled the median progression-free survival (PFS).