Phase II trial aiming to evaluate the clinical interest of Abemaciclib monotherapy in patients with locally advanced/metastatic head and neck cancer after failure of platinum and Cetuximab or anti-EGFR-based therapy and harboring an homozygous deletion of cdkn2a, and/or an amplification of CCND1 and/or of CDK6. Here, CDK6 is linked to head and neck cancer.