SummaryThis study of children and adults with acute lymphoblastic leukaemia (ALL) is the largest series of patients with hypodiploidy (<46 chromosomes) yet reported. The incidence of 5% was independent of age. Patients were subdivided by the number of chromosomes; near-haploidy (23-29 chromosomes), low hypodiploidy (33-39 chromosomes) and high hypodiploidy (42-45 chromosomes). The near-haploid and low hypodiploid groups were characterized by their chromosomal gains and a doubled hyperdiploid population. Structural abnormalities were more frequent in the low hypodiploid group. Near-haploidy was restricted to children of median age 7 years (range 2-15) whereas low hypodiploidy occurred in an older group of median age 15 years (range 9-54). Patients with 42-45 chromosomes were characterized by complex karyotypes involving chromosomes 7, 9 and 12. The features shared by the few patients with 42-44 chromosomes and the large number with 45 justified their inclusion in the same group. Survival analysis showed a poor outcome for the near-haploid and low hypodiploid groups compared to those with 42-45 chromosomes. Thus cytogenetics, or at least a clear definition of the modal chromosome number, is essential at diagnosis in order to stratify patients with hypodiploidy into the appropriate risk group for treatment.

High hyperdiploidy (HeH) (51 to 65 chromosomes) is found in one third of children with acute lymphoblastic leukemia and is associated with a good prognosis. Cytogenetic features may further refine this prognosis and identify patients with a poor outcome. We examined the effect of sex, age, individual trisomies, modal number, and structural abnormalities on survival among 700 children with HeH. Univariate analysis showed that age. sex, +4, +10, +18, and a high modal number were associated with survival. Multivariate analysis however, revealed that only age, sex, +4, and +18 were independent indicators. Hazard scores for predicting relapse and mortality were constructed. Three risk groups with 5-year event-free survival (EFS) rates of 86%, 75%, and 50% (P <.0001) were identified. The high-risk group comprised boys older than 9 years, boys aged 1 through 9 years without +18, and girls older than 9 years without +18, while girls aged 1 through 9 years with +18 had the best EFS. In terms of mortality, those younger than age 10 years with both +4 and +18 had an improved survival (96% vs 84% at 5 years, P <.0001). These findings confirm that the outcome of children with HeH is heterogeneous and that specific trisomies can identify patients with the greatest and least risk of treatment failure.

In myeloma, the prognostic impact of different strategies used to detect chromosome 13 deletion (D13) remains controversial. To address this, we compared conventional cytogenetics and interphase fluorescence in situ hybridization (iFISH) in a large multicenter study (n ¼ 794). The ability to obtain abnormal metaphases was associated with a poor prognosis, which was worse if D13, p53 deletion or t(4;14) was present, but only D13 remained significant on multivariate analysis. Patients with D13, by either cytogenetics or iFISH, had a poor prognosis. However, when cases with D13 detectable by both cytogenetics and iFISH were separated from those detected by iFISH only, the poor prognosis of iFISH-detectable D13 disappeared; their outcome matched that of patients with no detectable D13 (P ¼ 0.115). Addition of ploidy status to iFISH-D13 did not affect the prognostic value of the test. Indeed both cytogenetics and iFISH D13 divided both hyperdiploidy and nonhyperdiploidy into two groups with similar prognoses, indicating that the poor prognosis of ploidy is entirely due to its association with D13. We conclude that D13 detected by metaphase analysis is a critical prognostic factor in myeloma. Absence of D13, even in those patients yielding only normal or no metaphases, is associated with a relatively good prognosis.