Heterogeneity of hyperdiploid (51-67) childhood acute lymphoblastic leukemia

We studied the fully banded chromosomes of 182 children with hyperdiploid (51-67) acute lymphoblastic leukemia (ALL) to better delineate the heterogeneity of this disease subtype. Forty-six percent of the cases had numerical changes exclusively, while the remainder had structural as well as numerical changes. Chromosome 21 was added most often (97% of cases), followed by chromosomes 6 (86%), X (81%), 14 (80%), 4 (76%), 18 (68%), 17 (68%), 10 (56%), 8 (34%) and 5 (26%). Chromosomal translocations, including the t(1;19)(q23;p13) and t(9;22)(q34;q11), were detected in only 20% of the cases, as compared with 50% in ALL in general. The most common structural alterations were duplication of the 1q arm and isochromosome of 17q, present in 25 (14%) and nine (5%) cases, respectively. The presence of absence of structural abnormalities in these cases did not influence event-free survival, as assessed in 168 patients enrolled in three successive protocols for children with newly diagnosed ALL. By contrast, patients with 51-55 chromosomes per leukemic cell (n=105) appeared to fare worse than the 56-67 subgroup (n=63) (5-year probability of event-free survival = 72 +/- 5% (s.e.) vs 86 +/- 5%; P=0.04 by the stratified log-rank test). The poorer prognosis of the 51-55 subgroup was partly due to the higher frequency of isochromosome of 17q; 6/7 patients with the isochromosome in this group have had an adverse event. Other unfavorable features within the hyperdiploid (51-55) ALL subgroup include a low prevalence of trisomies of chromosomes 4 and 10 and a higher proportion of patients with leukocyte counts greater than 50 X 10(9)/l when compared to hyperdiploid (56-67). Thus, ALL defined by 51-55 chromosomes appears to be a clinicobiologic entity quite distinct from cases with higher modal numbers.