PECAM-1 is also expressed on various types of leukemias, including acute myeloid leukemia (AML) (8), acute lymphoblastic leukemia (ALL) (9), and chronic lymphocytic leukemia (CLL) (10,11), and has been implicated in prognosis of CLL, although it remains controversial. Here, PECAM1 is linked to acute lymphoblastic leukemia.