Many patients who have molecular evidence of the bcr-abl fusion gene, which characterizes the Ph1, have no evidence of the abnormal chromosome by cytogenetics. The bcr-abl fusion gene may be detectable only by fluorescence in situ hybridization (FISH) or reverse-transcriptase polymerase chain reaction (RT-PCR) because many patients have a different fusion protein from the one found in CML (p190 vs. p210). These tests should be performed, whenever possible, in patients with ALL, especially in those with B-cell lineage disease.
L3 ALL is associated with a variety of translocations that involve translocation of the c-myc proto-oncogene to the immunoglobulin gene locus t(2;8), t(8;12), and t(8;22).
Patients with ALL may present with a variety of hematologic derangements ranging from pancytopenia to hyperleukocytosis. In addition to a history and physical, the initial workup should include:
- Complete blood count with differential.
- A chemistry panel (including uric acid, creatinine, blood urea nitrogen, potassium, phosphate, calcium, bilirubin, and hepatic transaminases).
- Fibrinogen and tests of coagulation as a screen for disseminated intravascular coagulation.
- A careful screen for evidence of active infection.
A bone marrow biopsy and aspirate are routinely performed even in T-cell ALL to determine the extent of marrow involvement. Malignant cells should be sent for conventional cytogenetic studies, as detection of the Ph1 t(9;22), myc gene rearrangements (in Burkitt leukemia), and MLL gene rearrangements add important prognostic information. Flow cytometry should be performed to characterize expression of lineage-defining antigens and allow determination of the specific ALL subtype. In addition, for B-cell disease, the malignant cells should be analyzed using RT-PCR and FISH for evidence of the bcr-abl fusion gene. This last point is of utmost importance, as timely diagnosis of Ph1 ALL will significantly change the therapeutic approach.
Diagnostic confusion with AML, hairy cell leukemia, and malignant lymphoma is not uncommon. Proper diagnosis is crucial because of the difference in prognosis and treatment of ALL and AML. Immunophenotypic analysis is essential because leukemias that do not express myeloperoxidase include M0 AML, M7 AML, and ALL.
The examination of bone marrow aspirates and/or biopsy specimens should be done by an experienced oncologist, hematologist, hematopathologist, or general pathologist who is capable of interpreting conventional and specially stained specimens.