Case 1, a 50-year-old female with relapsed MS about five years post-HSCT for AML, presented with a right breast mass with CEBPA (VAF 11%), IDH2 (VAF 40%), and NPM1 (VAF 39%) mutations while bone marrow at that time did not show any mutations. The gene discussed is CEBPA; the disease is myeloid sarcoma.