CD274 and chordoma: Six chordoma cell lines; established from 3 from clival tumor patients (UM-Chor1, MUG-CC1, UM-Chor5), and 3 sacral tumor patients (JHC7, U-CH1, U-CH2) were analyzed by flow cytometry to quantify expression surface markers MHC-I/HLA-A,B,C, PD-L1, and EGFR.