We then investigated by immunohistochemistry of formalin-fixed paraffin-embedded (FFPE) tissue samples collected at diagnosis from 60 ALL patients (36 B-ALL and 24 T-ALL) for protein expression of Chk1, phosphorylated Chk1 (Ser345), Chk2, phosphorylated Chk2 (Thr68), Cdc25C, phosphorylated Cdc25C (Ser 2016), and phosphorylated H2A.X (Ser139) (γ-H2A.X). Here, CHEK1 is linked to acute lymphoblastic leukemia.