B-cell Acute Lymphoblastic Leukemia

B-cell Acute Lymphoblastic Leukemia (B-ALL)

Definition:

A hematologic malignancy characterized by uncontrolled proliferation of immature B-cell lymphoblasts in the bone marrow, blood, and extramedullary sites. It represents the majority (~75–80%) of ALL cases, in both pediatrics and adults.

Epidemiology

• Most common childhood cancer (peak incidence: 2–5 years).
• In adults: less common but associated with worse prognosis.

Pathophysiology

• Malignant transformation of B-cell precursors due to genetic alterations (chromosomal translocations, hyperdiploidy, hypodiploidy, oncogene rearrangements).
• Leads to:
  • Marrow failure (anemia, neutropenia, thrombocytopenia).
  • Organ infiltration (lymph nodes, liver, spleen, CNS, testes).

Common Genetic Abnormalities

• Favorable (pediatrics): ETV6-RUNX1 (t(12;21)), hyperdiploidy.
• Poor prognosis (adults & high-risk pediatrics):
  • BCR-ABL1 (Philadelphia chromosome, t(9;22))
  • KMT2A (MLL) rearrangements (infants)
  • Hypodiploidy
  • iAMP21 (intrachromosomal amplification of chromosome 21)

Clinical Presentation

• Bone marrow failure: fatigue (anemia), infections (neutropenia), bleeding/bruising (thrombocytopenia).
• Organ infiltration: hepatosplenomegaly, lymphadenopathy, bone pain.
• CNS/testicular involvement: more common in children.

Diagnosis

• Peripheral blood smear / bone marrow aspirate: lymphoblasts.
• Immunophenotyping (flow cytometry): CD19, CD10, CD22, CD79a, TdT (B-cell markers).
• Cytogenetics / molecular testing: defines risk and guides therapy (e.g., Ph+).

Treatment

• Multi-phase chemotherapy:
  1. Induction (steroids, vincristine, asparaginase ± anthracycline).
  2. Consolidation / Intensification (MTX, cytarabine, 6-MP, cyclophosphamide, asparaginase).
  3. Maintenance (6-MP, MTX, vincristine, steroids; 2–3 years in children).
• CNS prophylaxis: intrathecal MTX/ARA-C ± systemic high-dose MTX.
• Targeted therapies:
  • TKIs (Imatinib, Dasatinib, Ponatinib): for Ph+ ALL.
  • Blinatumomab (BiTE anti-CD19), Inotuzumab ozogamicin (anti-CD22 ADC), CAR-T (CD19-directed, e.g., Tisagenlecleucel) in relapsed/refractory disease.
• Stem Cell Transplant (Allo-SCT): for high-risk or relapsed patients, especially in adults.

Prognosis

• Children: excellent (long-term cure rates ~85–90%).
• Adults: worse (40–50% survival in younger adults; <20% in elderly).
• Prognosis guided by: age, WBC count at diagnosis, genetic profile, and MRD (minimal residual disease) response.

Pharmacy Pearl:

B-ALL is biologically distinct in pediatrics vs adults. Pediatric regimens are more curative, while adult regimens incorporate TKIs, CAR-T, and transplant earlier due to higher prevalence of poor-risk cytogenetics. Pharmacists play a key role in dosing (especially asparaginase, MTX, 6-MP), monitoring toxicities, and managing supportive care.