CDKN2A and Ewing sarcoma: Interestingly, although ES is a cancer of low mutational burden, 12% of patients have CDKN2A deletion (48) an event that often leads to co-deletion of MTAP. MTAP is an enzyme that is part of the methionine salvage pathway that metabolically converts methylthioadenosine (MTA) to methylthioribose (MTR) and adenine ultimately leading to methionine regeneration.