ULBP1 and Ewing sarcoma: Support for potential in vivo immune recognition of Ewing sarcoma tumours, however, was provided by immunohistochemical analysis of sequential Ewing sarcoma tumour samples demonstrating expression of (at least one of the) activating natural killer cell receptor ligands MICA and ULBP1 throughout all stages of disease and regardless of the histological response to chemotherapy.