Immunophenotypes and karyotypes of leukemic cells in children with Down syndrome and acute lymphoblastic leukemia.

PURPOSE: Immunophenotypes and karyotypes of leukemic cells were analyzed in a large series of Down syndrome patients with acute lymphoblastic leukemia (ALL) to examine the frequency of adverse prognostic features in comparison with other patients with ALL. PATIENTS AND METHODS: Presenting features and leukemic cell characteristics were compared for 76 patients with Down syndrome and 4,733 other patients with newly diagnosed ALL treated on protocols of the Pediatric Oncology Group (POG) and St Jude Children's Research Hospital (SJCRH). Treatment outcome was analyzed for the patients with non-T-cell disease enrolled on a single trial, for whom adequate follow-up data were available.
RESULTS: Down syndrome patients had lower platelet counts (P < .01) and were less likely to have an anterior mediastinal mass (P < .01) or CNS leukemia (P = .01). They were significantly more likely to have the pre-B immunophenotype (49% v 25.5%, P < .01) and less likely to have T-cell ALL (5.5% v 16%, P = .01). There was a notable absence among patients with Down syndrome of the t(4;11), t(1;19), and t(9;22), which are chromosomal translocations associated with an adverse prognosis in ALL. Treatment outcome did not differ significantly between patients with Down syndrome and the other children with non-T-cell ALL (P = .21); a third of the treatment failures in the former group resulted from treatment-related toxicities.
CONCLUSION: Children with Down syndrome and ALL had a low frequency of adverse clinicobiologic features at diagnosis. However, these findings did not translate into a superior outcome, apparently because of treatment-related toxicity in this group. Future trials should focus on pharmacokinetics and other strategies to reduce toxicity in these compromised patients.