Anatomic Pathology: Hematopathology

• The t(12;21) confers a good prognosis. The t(12;21) juxtaposes the ETV6 gene on 12p13 to the RUNX1 gene on 21q22. In addition to t(12;21), hyperdiploidy defined by more than 50 chromosomes also confers a good prognosis. Both t(12;21) and hyperdiploidy are commonly seen in young children. Both are not seen in infants, are seen at a decreasing frequency in older children, and are rare in adults.

• The t(9;22) translocation (A), t(4;11) translocation (B), and hypodiploidy (D) are all associated with a poor prognosis. In both children and adults with B-ALL, the t(9;22) confers the worst prognosis. The t(9;22) juxtaposes the BCR gene on 22q11.2 to the ABL1 gene on 9q34. The t(9;22) is more commonly seen in adults than in children and partially accounts for the worse prognosis seen overall in adults.

• The t(4;11) juxtaposes the MLL gene on 11q23 to the AF4 gene on 4q21. The t(4;11) is most commonly seen in infants and is associated with a high leukocyte count often more than 100,000 cells/μl, central nervous system involvement, and CD10 negativity.

• The t(1;19) previously was associated with a poor prognosis; however, with modern chemotherapy it is associated with an intermediate prognosis. The t(1;19) juxtaposes the E2A gene on 19p13.3 to the PBX gene on 1q23. The t(1;19) is associated with CD34 negativity (C).

• Hypodiploid B-ALL is defined by having less than 46 chromosomes. Within hypodiploid B-ALL, prognosis worsens with decreasing number of chromosomes.