Is Acute Lymphoblastic Leukemia (ALL) more common in children than in adults?

Acute Lymphoblastic Leukemia (ALL) is Significantly More Common in Children Than Adults

Yes, Acute Lymphoblastic Leukemia (ALL) is definitively more common in children than in adults, representing 75-80% of acute leukemias in children but only 20% of leukemias in adults. 1

Epidemiology of ALL Across Age Groups

ALL demonstrates a clear age-dependent distribution:

• ALL is the most common childhood cancer, constituting approximately 25% of cancer diagnoses among children under 15 years of age 2
• ALL remains the most common acute leukemia until the early 20s, after which acute myeloid leukemia becomes more prevalent 2
• The median age at diagnosis is 17 years, with 53.5% of patients diagnosed at <20 years of age 1
• The incidence rate of ALL is 1.8 per 100,000 individuals per year in the US 1

Cytogenetic Differences Between Pediatric and Adult ALL

The difference in ALL prevalence between children and adults is accompanied by significant differences in cytogenetic subtypes:

Favorable Cytogenetic Subtypes (More Common in Children)

• Hyperdiploidy (>50 chromosomes):
  • Present in 25% of pediatric ALL cases
  • Only 7% of adult ALL cases 3
• TEL-AML1 (ETV6-RUNX1) fusion gene:
  • Present in 22% of pediatric ALL cases
  • Only 2% of adult ALL cases 3
  • Associated with favorable outcomes 3

Unfavorable Cytogenetic Subtypes (More Common in Adults)

• Philadelphia chromosome (Ph-positive, BCR-ABL1):
  • Present in only 3% of pediatric ALL cases
  • Present in 25% of adult ALL cases 3
  • Frequency increases with age (up to 40% in patients >50 years) 3
  • Associated with poor prognosis 3

Outcomes by Age Group

The differences in cytogenetic profiles contribute to significant outcome disparities:

• Children: 80-90% long-term survival rates 4
• Adolescents and Young Adults (AYAs): 60-70% 5-7 year event-free survival rates 3
• Adults: 40-50% long-term survival rates 4
• European data: 5-year survival rates of 85.8% for ages 0-14,62.2% for ages 15-19, and 52.8% for ages 20-39 5

Clinical Implications

The higher prevalence of ALL in children and the different cytogenetic profiles have important treatment implications:

• Children generally have more favorable cytogenetic subtypes, contributing to better outcomes 3
• AYAs represent a unique population who may benefit from pediatric-inspired treatment protocols rather than adult regimens 5
• Treatment approaches should consider age-specific cytogenetic profiles, with more intensive regimens often needed for adults due to higher-risk disease features 4

Common Pitfalls in ALL Management

1. Misclassification of AYA patients: These patients may receive either pediatric or adult protocols depending on referral patterns, potentially affecting outcomes 3

2. Underestimating CNS involvement risk: Adults have historically shown higher rates of CNS involvement (27.7%) compared to children (7.1%) when receiving similar protocols 6

3. Overlooking MRD assessment: MRD status is critical for prognosis and should be evaluated upon completion of induction therapy, with MRD negativity defined as <0.01% 1

The significant difference in ALL prevalence between children and adults, along with the distinct cytogenetic profiles, underscores the importance of age-appropriate risk stratification and treatment approaches to optimize outcomes across all age groups.