Extramedullary leukemia in children with newly diagnosed acute myeloid leukemia: a report from the Children's Cancer Group.

Objectives: To describe features of patients with acute myeloid leukemia presenting with extramedullary leukemic tumors (EML).

Methods: Among 1,832 patients entered on Children's Cancer Group's chemotherapy trials with acute myeloid leukemia, 199 patients had EML, defined as any leukemic collection outside the bone marrow cavity. Three patient groups were denoted: group 1 (n=109) with EML involving skin (with or without other sites of EML), group 2 (n=90) with EML in sites other than skin, and group 3 (n=1,633) without EML.

Results: The incidence of EML was 10.9%. Group 1 patients tended to be younger, had higher white blood cell counts, were more often CNS positive, had FAB M4 or M5 subtypes, and possessed more abnormalities of chromosome 11 than group 3 patients. Group 2 patients were younger, more often had the FAB M2 subtype, and had a higher incidence of t(8;21)(q22;q22) abnormality than group 3, but had similar white blood cell counts and incidence of CNS positivity at diagnosis. For group 1 the 5-year event-free survival was 26%, significantly worse than for group 3 at 29%. Event-free survival was better for group 2 patients (5-year estimate 46%), which remained a favorable prognostic factor by multivariate analysis. The authors retrospectively determined whether 118 (59%) of the EML patients received localized radiotherapy to the site of EML: 42 did and 76 did not. There were no differences in estimated event-free survival between patients who did and did not receive radiotherapy.

Conclusions: Non-skin (group 2) EML appeared to be an independent favorable prognostic factor. Localized radiotherapy to the site of EML at the end of induction chemotherapy did not improve outcome.