CD274 and chordoma: Mathios detected the expression of PD-1 and PD-1 ligands in 10 chordoma specimens and 3 chordoma cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and found that PD-1 expressed on TILs, while PD-L1 expressed on both TILs and tumor-associated macrophages (TAMs) in 3/10 tumor specimens (40).