Review Question - QID 105420

Acute lymphoblastic leukemia (ALL) is the most common leukemia in children and is diagnosed by bone marrow biopsy showing >25% lymphoblasts. Terminal deoxynucleotidyl transferase (TdT) is positive in both normal pre-B and pre-T cells as well as the lymphoblasts seen in ALL.

ALL is a neoplasm of early lymphocytic precursors. Bone marrow biopsy reveals a predominance of lymphoblasts. The disease is most common in patients under the age of 15 and is the most common malignancy affecting this age group. Luckily, it is very responsive to therapy. Poor prognostic factors include age < 2 or > 9, WBC > 100,000, and CNS involvement. B-cell phenotype, increased LDH, and rapid leukemic cell proliferation are indicative of a high risk of CNS involvement. The disease may not only spread to the CNS, but also the testes. As always be aware of telltale signs of leukemia, which include recurrent infections, anemia, thrombocytopenia, and bleeding. TdT is a specialized DNA polymerase that results in random nucleotide insertion in pre-B and T cells and if important for affinity maturation. It is positive in both T and B cell ALL.

Abramson and Melton discuss the basics of clinical assessment of leukocytosis. Most often leukocytosis is due to relatively benign conditions such as infections or inflammatory processes. Physical stress and emotional stress, for example, may elevate a white blood cell count as can corticosteroids, lithium, and beta agonists. Primary bone marrow disorders, however, should be suspected in patients who present with extremely elevated white blood cell counts or concurrent abnormalities in red blood cell or platelet counts as well as clinical signs of weight loss, bleeding, bruising, hepatosplenomegaly, lymphadenopathy, and immunosuppression.

Teachey and Hunger discuss relapse risk prediction in children with ALL. Other than age and white blood cell count at presentation, many clinical variables previously used for risk group allocation are no longer prognostic, as minimal residual disease and the presence of sentinel genetic lesions are more reliable at predicting outcome. In the near future, patients will be stratified not just based on chromosomal translocations but also genomic signatures and clustering algorithms.

Illustration A depicts the characteristic lymphoblasts on peripheral smear in acute lymphoblastic leukemia.

Incorrect Answers:
Answer 1: Although the 9:22 translocation is most often remembered for its strong association with CML, it is indicative of a poor prognosis in children with ALL.
Answer 3: The 12:21 translocation is usually found in pediatric patients and represents a better prognosis.
Answer 4: Age greater than 9 or less than 2 are poor prognostic factors.
Answer 5: B-cell phenotype is associated with the risk of CNS involvement.