CTLA4 and histiocytic sarcoma: The expression of CTLA-4 on CD8+ lymphocytes was also significantly higher in the histiocytic sarcoma group (4.35% ± 1.37%) than in the other tumor group (1.32% ± 0.82%; P = 0.003) and the control group (0.62% ± 0.68%; P = 0.003; Fig 1B).