Nonrandom Involvement of the l2p12 Breakpoint in Chromosome Abnormalities of Childhood Acute Lymphoblastic Leukemia

We studied the presenting clinical and biologic features of 23 children with acute lymphoblastic leukemia (ALL) whose leukemic marrow karyotypes contained abnormalities involving the short arm of chromosome 12. Nineteen of the abnormalities were assigned to the 1 2pl 2 breakpoint. The median age of the children was 5 years (range 2 to 13 years) and their initial leukocyte counts ranged from 1,800 to 424 OOO/ML (median 3O,O00/ sL). Twenty-one patients (91 %) had common phenotype ALL (CALLA+ . HLA-DR +), including three cases with a pre-B cell phenotype (CIg +). The remaining two cases were T cell in origin. The FrenchAmerican-British (FAB) morphologic type of lymphoblastic leukemia was Li in all cases but one. With a median follow-up of 1 1 months, four patients have relapsed and another failed induction therapy. The modal chromosome number in all cases was <50. Three distinct cytogenetic