Over 75% of all childhood leukemias are acute lymphoblastic/lymphocytic leukemia (ALL). Most patients with ALL are between two and five years old. ALL is most often identified after a young patient fails to improve from a suspected minor illness, like a cold or flu. Extensive workups for Epstein-Barr virus (EBV), cytomegalovirus (CMV), and other viruses are often conducted in the search for an infectious source of the patient's symptoms. When such an infection is not found, a health care provider may become concerned about leukemia in the setting of prolonged fevers, bruising, enlarged lymph nodes, and/or hepatosplenomegaly (enlarged liver and spleen). All of those symptoms relate to bone marrow failure that results from the overproduction of lymphoblasts. Many children often complain of bone pain, especially in the legs.
Common laboratory features in ALL:
- Anemia
- Neutropenia
- Thrombocytopenia
- Normal WBC count
- Lymphoblasts in the peripheral blood
Classifying ALL:
- Traditional classification of ALL was done using the French-American-British (FAB) system, which classified ALL based on lymphoblast size and nucleus/cytoplasm characteristics. The FAB system is no longer used in diagnosis or treatment decisions.
- Two general categories of lymphoblastic leukemia exist in the World Health Organization (WHO) classification system. These categories are based upon the actual cell lineage of the lymphoblasts - either precursor B cell acute lymphoblastic leukemia or precursor T cell acute lymphoblastic leukemia.
- It is impossible to distinguish between precursor B and T cell ALL from visual observation of the peripheral smear or bone marrow aspirates.
- Immunophenotyping using monoclonal antibodies is utilized to identify cluster of differentiation (CD) markers on the lymphoblast cell surface, with the vast majority (nearly 80%) of childhood ALL being identified as precursor B cell ALL.
