Acute Lymphoblastic Leukemia

Chapter: Acute Lymphoblastic Leukemia
McMaster Section Editor(s): Mark Crowther
Section Editor(s) in Interna Szczeklika: Andrzej Hellmann, Bogdan Ochrem
McMaster Author(s): Mark Crowther
Author(s) in Interna Szczeklika: Jerzy Hołowiecki
Additional Information

Definition, Etiology, Pathogenesis Top

Acute lymphoblastic leukemia (ALL)/lymphoblastic lymphoma (LBL) are malignancies originating from B-lymphocyte or T-lymphocyte precursor cells (lymphoblasts). The lymphoblasts are present mainly in bone marrow and peripheral blood (B-cell ALL, T-cell ALL), or less frequently in lymph nodes and extranodal sites (B-cell LBL, T-cell LBL). In children <15 years, ALL/LBL constitute ~25% of all malignancies and ~75% of all leukemias. In adults, they usually develop before 30 years of age and account for ~20% of acute leukemias.

The 2008 World Health Organization classification is based on the cell origin and biology. In B-cell and T-cell subtypes, genetically and molecularly distinct clinical entities are defined, while other types are jointly classified as “ALL/LBL, not otherwise specified.” Burkitt-type ALL is a leukemic manifestation of Burkitt lymphoma, which is currently classified as a mature B-cell malignancy.

The immunophenotypic classification is of key importance for clinical practice. It includes:

1) B-cell ALL: Pro-B (pre-pre-B) ALL, common ALL (CD10+, the most frequent type), pre-B ALL.

2) T-cell ALL: Pro-T and pre-T ALL (CD1a, cyCD3+), cortical ALL (CD1a+, relatively good prognosis), medullary T-cell ALL (CD1a, sCD3+).

Clinical Features And Natural History Top

1. Signs and symptoms are similar to acute myeloid leukemia, but lymphadenopathy, splenomegaly, or both are observed in as many as 50% of patients, and manifestations of the involvement of erythropoietic and megakaryopoietic lineages are less severe. Twenty five percent of patients develop bone and joint pain. Central nervous system (CNS) involvement is relatively more common than in AML and ranges from 3% in B-cell ALL to 8% in T-cell ALL. In patients with T-cell ALL, mediastinal lymph node enlargement as well as high white blood cell (WBC) counts are frequent.

2. Natural history: In patients with early disease, the abnormalities may be limited to the complete blood count (CBC). Patients with advanced disease present with bleeding, infection, or with signs of CNS, mediastinal, and other organ involvement, which untreated lead to death within a few weeks.

Diagnosis Top

Diagnostic Tests

1. CBC: Leukopenia may be observed in patients with certain subtypes of ALL (particularly in early disease); leukocytosis (very high and rapidly increasing in patients with T-cell ALL subtypes). In ~25% of patients with pro-B ALL, WBC counts are >100,000 cells/microL. Anemia, neutropenia, and thrombocytopenia are usually seen. Lymphoblasts are found in peripheral blood. Eosinophilia may be also present (in T-cell ALL).

2. Bone marrow examination: Bone marrow aspiration with microscopic examination and immunophenotyping.

3. Immunophenotyping using flow cytometry (peripheral blood or bone marrow) is the basis for confirming the diagnosis and the immunophenotypic classification, which facilitates the assessment of prognosis as well as identification of the abnormalities that are used in monitoring minimal residual disease (MRD) during treatment.

4. Cytogenetic and molecular studies: In the majority of patients with ALL, lymphoblasts have an abnormal karyotype, including abnormalities in the chromosome numbers and structure. Cytogenetic abnormalities associated with an adverse prognosis include t(4;11), low hypodiploidy, and a complex karyotype (≥5 abnormalities). Translocation t(9;22), also termed the Philadelphia (Ph) chromosome, is found in 20% to 30% of all ALL cases, more frequently in patients with common ALL and in elderly patients (up to 50%), and is associated with the highest risk. MLL gene rearrangements are similarly associated with an adverse prognosis. Quantitative molecular studies (real-time quantitative polymerase chain reaction) are also used for MRD monitoring (eg, identification of the BCR-ABL1 fusion gene in patients with Ph+ ALL).

5. Imaging studies: In ~50% of patients with T-cell ALL subtypes, upper mediastinal mass caused by the involvement of the thymus and mediastinal lymph nodes is seen. Imaging is useful in assessing the size of the lymph nodes and the spleen.

6. Lumbar puncture: In the case of CNS involvement, lumbar puncture may reveal increased cerebrospinal fluid cell counts with blasts detected by cytologic examination.

Diagnostic Criteria

Bone marrow microscopy and immunophenotyping are essential for diagnosis. The presence of lymphoblasts must be documented and ≥2 B-cell or T-cell markers must be found to confirm the diagnosis. In ~20% of patients, features of LBL are predominant, with infiltrates affecting mainly lymph nodes and <20% to 25% blasts in bone marrow; in such cases examination of a lymph node may be necessary.

Differential Diagnosis

Poorly differentiated AML; infectious mononucleosis; other viral infections, particularly causing lymphocytosis, thrombocytopenia, or hemolytic anemia; other conditions causing pancytopenia; non-Hodgkin lymphomas.

Treatment Top

1. Initial treatment is aimed at decreasing the leukemic cell burden to reduce the risk of tumor lysis syndrome; this may involve the use of prednisone or dexamethasone. Prophylaxis of tumor lysis syndrome should be provided to all patients initiating therapy.

2. Remission induction is aimed at removing the tumor burden; this includes multiagent combination chemotherapy regimens (eg, vincristine, an anthracycline, glucocorticoids [prednisone or dexamethasone], and pegylated asparaginase; usually for 4 weeks).

3. Remission consolidation is aimed at removing MRD; this includes sequential cycles of high-dose or intermediate-dose antineoplastic agents.

4. Postconsolidation treatment:

1) In standard-risk patients and in patients who are not eligible for hematopoietic stem cell transplantation (HSCT), maintenance treatment is continued for 2 years, provided the MRD-negative status is maintained.

2) In high-risk patients (>80% of adult patients), allogeneic HSCT from a human leukocyte antigen (HLA)-compatible sibling or an unrelated donor should be considered. If no donors are available, consider autologous HSCT.

5. Treatment of Ph+ ALL: Chemotherapy combined with tyrosine kinase inhibitors (TKIs) (imatinib, dasatinib) with the goal of allogeneic HSCT in patients who qualify for this therapy.

6. Prevention and treatment of CNS involvement: For all patients, remission-induction and usually also remission-consolidation therapies require either CNS treatment, prophylaxis with intrathecal chemotherapy, or both, as well as—depending on the risk profile, age, and comorbidities—CNS radiation.

7. Management of patients with no response to the first-line treatment or with relapses: New agents (above), drugs with no cross-resistance with the first-line agents, other drug combinations, HSCT.

8. Supportive treatment as in acute myeloid leukemia.

Prognosis Top

Risk groups:

1) Standard-risk group:

a) Age <35 years.

b) WBC <30,000 cells/microL in B-cell ALL or <100,000 cells/microL in T-cell ALL.

c) Immunophenotype: Common/pre-B ALL or cortical (CD1a+) T-cell ALL.

d) Complete remission (CR) achieved within <4 weeks.

2) High-risk group: All patients not included in points 1) and 3).

3) Very high-risk group: Karyotype t(9;22) [Ph+, BCR-ABL1+].

The importance of the risk groups may change in the course of treatment. Apart from the above cytogenetic abnormalities, the most important adverse prognostic factor that is the basis for the classification of patients into standard-risk and high-risk groups is the MRD status monitored using cytogenetic or molecular studies at subsequent stages of treatment. CR is achieved in >90% of adult patients with ALL. Overall 5-year survival rates in adults: 54% in patients <30 years of age; 35% in patients 30 to 44 years of age; 24% in patients 45 to 60 years of age; and 13% in patients >60 years of age.

Patients with the Ph chromosome have a particularly poor prognosis with respect to both CR duration and overall survival. In such cases, treatment with TKIs and early allogeneic HSCT should be considered.

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