Cytogenetic Variation of B-Lymphoblastic Leukemia with Intrachromosomal Amplification of Chromosome 21 (iAMP21): A Multi-Institutional Series Review

Objectives: B-lymphoblastic leukemia (B-ALL) with intrachromosomal amplification of chromosome 21 (iAMP21) is a relatively uncommon manifestation of acute leukemia and limited predominantly to the pediatric population. Case-specific information regarding flow cytometric, morphologic, and laboratory findings of this subtype of leukemia is currently lacking. Methods: We searched the databases of three large institutions for lymphoblastic leukemia with iAMP21 from 2005 through 2012 and analyzed the clinicopathologic features. Results: We identified 17 cases with five or more RUNX1 signals on interphase nuclei, 14 of which were consistent with the Children's Oncology Group (COG) definition for iAMP21-namely, the presence of three or more RUNX1 signals on one marker chromosome. These cases showed a statistically significant lower peripheral WBC count and older age at diagnosis compared with all pediatric cases of B-ALL. We also identified three cases with increased RUNX1 signals scattered on multiple marker chromosomes that did not meet the COG definition of iAMP21 but showed similar 21q instability and older age at presentation. Conclusions: Our findings not only demonstrate that B-ALL with iAMP21 is truly a distinct clinicopathologic entity but also suggest that a subset of cases of B-ALL with iAMP21 can show variable cytogenetic features.