Most Cases of Acute Lymphoblastic Leukemia Affect B-Cell Lineage
The vast majority of ALL cases affect the B-cell lineage, accounting for approximately 88% of childhood cases and 75% of adult cases, making B-cell ALL (Answer A) the correct answer. 1
Epidemiologic Distribution by Lineage
B-Cell Lineage Predominance
- B-cell lineage ALL constitutes approximately 88% of pediatric ALL cases, representing the overwhelming majority of childhood leukemia 1
- In adult patients, B-cell lineage ALL accounts for approximately 75% of cases (including mature B-cell ALL which constitutes 5% of adult ALL) 1
- This includes all B-cell subtypes: precursor-B-cell ALL (pro-B, common B, and pre-B) and mature B-cell ALL 1
T-Cell Lineage Minority
- T-cell lineage ALL represents only 12% of childhood ALL cases 1
- In adults, T-cell ALL constitutes approximately 25% of cases, which is higher than in children but still the minority 1
Clinical Significance of Lineage Distribution
Why B-Cell Predominance Matters
- The B-cell origin determines treatment approach, as most ALL protocols are designed primarily for B-cell disease 1
- B-cell ALL has distinct immunophenotypic markers (CD19, CD22, CD79a, CD10) that guide diagnosis and targeted therapy 1
- Most favorable cytogenetic abnormalities (hyperdiploidy, TEL-AML1/ETV6-RUNX1) occur exclusively in B-cell lineage ALL 1
Age-Related Patterns
- The B-cell predominance is even more pronounced in younger children (1-9 years), where it approaches 90% of cases 1
- The relative proportion of T-cell ALL increases slightly with age but never exceeds B-cell ALL frequency 1
Common Pitfall to Avoid
Do not confuse the most common lineage (B-cell) with the most common chromosomal abnormality. While B-cell ALL is most common overall, specific cytogenetic subtypes vary by age—hyperdiploidy (25%) and ETV6-RUNX1 (25%) are most common in children, while Philadelphia chromosome t(9;22) becomes more common in adults (25%) but still within the B-cell lineage context 1.