In this context, the study proposal is to evaluate the clinical interest of a monotherapy with a PI3K inhibitor (BKM120, Novartis) in patients with metastatic head and neck cancers refractory or relapsing under platin and cetuximab based- chemotherapy. Since resistance to cetuximab can result from phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) mutation, PIK3CA amplification or mutation upstream in the PI3K pathway, BKM120 activity will be evaluated in two parallel independent cohorts of patients: patients presenting a PI3KCA mutation and patients without a PI3KCA mutation.