Cytogenetic analysis of bone marrow. (a) The G-banded metaphase cell demonstrates abnormalities involving chromosomes 2 and 22 (black arrows), interpreted to represent an initial chromosome 2 pericentric inversion that disrupts the ALK gene at band 2p23 and translocates the centromeric portion of the gene to band 2q22. This is followed by a translocation between the inverted chromosome 2 (with a breakpoint distal to the ALK gene) and chromosome 22q. The karyotype is designated as 46,XX,inv(2)(p23q22)t[inv(2);22)(p24;q12)]. (b) Fluorescence in situ hybridization (FISH) utilizing an ALK gene break-apart probe demonstrates disruption of the gene (white arrow) and relocation of the centromeric portion of the gene to the long arm of chromosome 2 (white arrow head) as a result of the chromosome 2 pericentric inversion.