CDK4/6 Inhibitors as Upfront Treatment in a Patient with Breast Cancer Presenting with a Clinical Critic Situation: A Case Report and Review of the Literature.

CDK4/6 inhibitors have revolutionized the treatment algorithm of luminal metastatic breast cancer, becoming the recommended first-line therapy in association with endocrine therapy. However, due to its theoretically greater and more rapid tumor shrinkage, the upfront use of chemotherapy is considered in some clinical situations like visceral crisis. At the state of the art level, a paucity of data is available about the use of CDK4/6 inhibitors in patients presenting with visceral crisis or with life-threatening conditions since this population was historically excluded from clinical trials. In addition, data regarding direct comparison between combinations of chemotherapy and CDK4/6 inhibitors in terms of efficacy, rapidity of responses and long-term outcomes are lacking. We report the case of a 68-year-old woman with luminal metastatic breast cancer presenting at diagnosis with a critical and potentially life-threatening condition. The patient was treated with first-line Abemaciclib plus letrozole and achieved a rapid partial response with sudden clinical stabilization. Although the patient did not technically present with a visceral crisis, this case presentation also endorsed the upfront use of CDK4/6 inhibitor combinations in critical clinical situations in the absence of severe organ dysfunction and after multidisciplinary discussion.