Thiopurine S-methyltransferase (TPMT) polymorphisms in children with acute lymphoblastic leukemia, and the need for reduction or cessation of 6-mercaptopurine doses during maintenance therapy: the Polish multicenter analysis - Peregud-Pogorzelski, J; Tetera-Rudnicka, E; Kurzawski, M (Pediatr Blood Cancer, 2011)