Leukemia, Acute Lymphoblastic (ALL) in Adults
- ALL in adults is the result of a clonal proliferation, survival, and impaired differentiation of immature lymphocytes. The World Health Organization (WHO) defines ALL as the presence of ≥25% lymphoblasts in the bone marrow, and the National Comprehensive Cancer Network (NCCN) uses a ≥20% as cutoff.
- ALL and lymphoblastic lymphoma (LBL) can arise from same precursor cell line and be considered diseases along the same spectrum:
- LBL presents as a mass, possibly, but not limited to, the mediastinum, with <25% blasts in the bone marrow.
- ALL may present with a mass lesion but contains ≥25% bone marrow involvement.
- Any organ can be affected.
Many chemotherapy (CTX) drugs are teratogenic.
ALL is the most common malignancy in children—it accounts for 30% of all pediatric malignancies and 80% of pediatric leukemias (see “Acute Lymphoblastic Leukemia, Pediatric”).
Patients >60 years with ALL have a 42% mortality during induction CTX. The cause of death is usually CTX-related complications or relapse. Survival is often reduced due to poor tolerance of CTX, thus leading to dose reductions and ineffective medication delivery.
- Incidence of ALL is 1.8/100,000 per year.
- Higher incidence in older age, males, whites, those with history of radiation, CTX, or certain genetic disorders
- Prevalence of ALL can range from 15% to 50% and increases with age.
- Bimodal distribution: early peak in childhood, second peak at around age 50
- 75–80% of cases occur in children, approximately 20% in adults.
Etiology and Pathophysiology
The pathophysiology of ALL involves the abnormal proliferation and differentiation of clonal lymphoid cells.
- Higher rates in monozygotic and dizygotic twins
- Increased risk of ALL with diseases related to chromosomal instability and inherited chromosomal abnormalities
- Age >70 years, radiation and CTX exposure, and infection with HIV are risk factors for developing ALL.
- Human T-cell lymphotropic virus type 1 is associated with adult T-cell ALL.
- Epstein-Barr virus is associated with mature B-cell ALL.
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