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    Adult Acute Lymphoblastic Leukemia Treatment (PDQ®): Treatment - Health Professional Information [NCI] - General Information About Adult Acute Lymphoblastic Leukemia (ALL)

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    Molecular Genetics

    It has been recognized for many years that some patients presenting with acute leukemia may have a cytogenetic abnormality that is cytogenetically indistinguishable from the Philadelphia chromosome (Ph1).[3] The Ph1 occurs in only 1% to 2% of patients with acute myeloid leukemia (AML), but it occurs in about 20% of adults and a small percentage of children with ALL.[4] In the majority of children and in more than one-half of adults with Ph1-positive ALL, the molecular abnormality is different from that in Ph1-positive chronic myelogenous leukemia (CML).

    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).

    Diagnosis

    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:

    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.

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