Endocrine therapy represents the basis for the treatment of estrogen receptor-positive breast cancer, but several tumors harbor intrinsic resistance and acquired resistance to endocrine therapy is inevitable in metastatic disease. Combination strategies of endocrine therapy with targeted agents are aimed to overcome endocrine resistance. The selective CDK4/6 inhibitor palbociclib has shown promising results in metastatic luminal breast cancer when used in combination with endocrine therapy both in the first-line setting as in pretreated women. The drug showed a manageable safety profile with uncomplicated neutropenia as the most frequent side effect. Approval was already granted in the US and is also awaited during 2016 for Europe.
Keywords: Abemaciclib; CDK4/6 inhibitors; Endocrine resistance; Palbociclib; Ribociclib.