reported the PD-1.9 C/T genotype as associated with a decreased risk of leukemia (OR = 0.43) (169), however, taking into consideration the fact that only 59 leukemia patients (28 acute myeloid leukemia, 20 acute lymphocytic leukemia, 11 chronic myelogenous leukemia) and 46 controls were enrolled in this study, these results should be interpreted warily. Here, PDCD1 is linked to leukemia.