Prognostic impact of peripheral blood white blood cell count (WBC) at the diagnosis of childhood acute
lymphoblastic leukaemia (ALL) was evaluated in a population-based consecutive series of 2666 children
aged 1–15 treated for ALL between 1992 and 2008 in the five Nordic countries (Denmark, Finland, Iceland,
Norway and Sweden). Ten-year event-free (pEFS10y) survival and overall (pOS10y) survival were
0.75 ± 0.01 and 0.85 ± 0.01, respectively. Although treatment intensity was determined by WBC, nonremission
and relapsed patients still had significantly higher WBC than those in remission for B-cell precursor
(BCP) (median WBC: 24.8 vs. 14.0 vs. 8.3 · 109 / L, P < 0.001), but not for T-lineage (T-ALL) (median
WBC: 127.8 vs. 113.0 vs. 86.8 · 109 / L, P = 0.22). pEFS was inversely related to WBC for BCP
(P < 0.001), but not for T-ALL. WBC was not associated with risk of event for BCP or T-ALL for patients
with minimal residual disease at the end of induction (MRDd29) <10)3. In contrast, for MRDd29 ‡ 10)3 and
<5% leukaemic blasts in bone marrow at day 29, the pEFS5y for WBC < 100.0 (N = 152) vs. ‡100.0
(N = 19) was 0.76 vs. 0.50 (P = 0.001). That was the case both for BCP (pEFS5y 0.76 vs. 0.58) and for
T-ALL (pEFS5y 0.71 vs. 0.38). Whether the inferior EFS for the subset of patients with high WBC and slow
initial response to treatment reflects rare or overlooked cytogenetic aberrations as well as the factors that
determine WBC levels at diagnosis awaits exploration.