Table 1. Patient characteristics and event rate in relation to thiopurine methyltransferase activity.

	High activity	Intermediate activity	P
Patient distribution
No. of patients	362	49
Male/female	192/170	28/21	0.59
Standard risk/Intermediate risk	200/162	24/25	0.41
Pharmacologyb/control groupc	176/186	27/22	0.39
Median (50 % range)
Age at diagnosis, years	4.0 (2.9-6.0)	4.5 (3.2-6.4)	0.11
WBC at diagnosis, × 109/L	6.0 (3.0-13.0)	5.0 (2.0-11.5)	0.46
Survival outcomes
Dead in CR1	2	0
SMN	2	2
Relapse	54	4
pEFS at 15 years (± SE)	83.8 (2.0)	87.4 (4.8)	0.47

^aPatients were classified as TPMT high activity if TPMT was >14 IU/ml and TPMT intermediate activity if TPMT was <14 IU/ml. Patients with TPMT deficiency (n=2) were excluded from the study.

^bPharmacology group had dose adjustments by red blood cell levels of MTX and 6MP metabolites in addition to dose adjustments by toxicity.

^cControl group, see text and Schmiegelow et al., 2003.

Dead in CR1, dead in first complete remission; SMN, second malignant neoplasm; pEFS, probability of event-free survival; SE, standard error.