Involvement of der(12)t(12;21)(p13;q22) and as well as additional rearrangements of chromosome 12 homolog in ETV6/RUNX1-positive acute lymphoblastic leukemia.

The t(12;21) translocation is the most common translocation in childhood B-precursor ALL. Because G-banding cannot detect the cryptic t(12;21), the full characterization of additional aberrations involving chromosome 12 is often difficult. Spectral karyotyping (SKY) can distinguish a der(12)t(12;21) chromosome from a nonrearranged chromosome 12. We therefore applied SKY on an unselected series of 14 patients after G-banding analysis for the detection of additional chromosomal rearrangements and especially for aberrations involving chromosome 12. Chromosome 12 was the most frequently affected by structural aberrations, with involvement of both homologs. Structural aberrations of der(12)t(12;21) in addition to the typical t(12;21) were found in five patients and structural aberrations of the nonrearranged chromosome 12 were found in four patients. This study points to the susceptibility of der(12)t(12;21) and the other chromosome 12 homolog to further rearrangement.