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12p chromosomal aberrations in precursor B childhood acute lymphoblastic leukemia predict an increased risk of relapse in the central nervous system and are associated with typical blast cell morphology.

Recently we reported cytogenetic, clinical, and immunologic data of 135 childhood ALL patients, who were diagnosed and treated in The Sophia Children's Hospital between January 1, 1980 and November 1, 1990. An increased risk for a first relapse in the central nervous system (CNS) was detected in a subgroup of childhood ALL patients with common ALL or pre-B ALL phenotype and chromosomal aberrations of the short arm of chromosome 12. In this paper we report clinical, cytogenetic, immunologic, morphologic and cytochemical data on these eight childhood ALL patients with aberrations of the short arm of chromosome 12 and of an additional four cases that were diagnosed and treated between November 1, 1990 and February 1, 1992. We found that three out of six common ALL, two out of three pre-B ALL and one out of three T-ALL patients with 12p chromosomal rearrangements developed a first relapse in the CNS. On the contrary, the frequency of CNS relapse in our childhood ALL patients without 12p aberrations was 10%. Furthermore, morphologic and cytochemical analysis of the bone marrow smears of these 12 patients with aberrations of the short arm of chromosome 12 revealed that the nine cases with pre-B or common ALL phenotype had typical morphologic characteristics that are unusual for newly diagnosed childhood ALL. Typical for this subtype is the presence of large polymorphic blast cells without nucleoli. The nuclei are irregularly shaped showing folds and clefts and a stripy pattern. The nucleus and cytoplasm are often abundantly vacuolated. The cytoplasm has a foamy light-blue appearance.