Acute lymphoblastic leukemia (ALL) is one of those Step-friendly diagnoses where a few core facts (age, immunophenotype, genetics, and key complications) let you crush questions fast. Below is a quick-hit, shareable comparison table plus mnemonics and one-liners to lock it in.
The 10-second gist (what to picture on test day)
Think: kid with bone pain + infections + bleeding, labs show blasts, smear may show TdT+ lymphoblasts, and genetics often point to good vs bad prognosis.
One-liner:
ALL = malignant proliferation of immature lymphoid precursors (lymphoblasts), classically in children, causing marrow failure and sometimes a mediastinal mass (T-ALL).
Visual/Mnemonic device (fast recall)
“ALL = A.L.L.”
- A = Age: kids (most common pediatric leukemia)
- L = Lymphoblasts: TdT+, CD10+ (B-ALL) or CD3+ (T-ALL)
- L = Lump in chest: anterior mediastinal mass (especially T-ALL, thymic)
Micro-visual:
- B-ALL → “Bone marrow + B-cell markers”
- T-ALL → “Thymus + T-cell markers” → mediastinal mass
Comparison table: Acute lymphoblastic leukemia (ALL)
High-yield ALL subtypes & testable differences
| Feature | B-ALL (most common) | T-ALL |
|---|---|---|
| Typical age | Children (peak ~2–5) | Adolescents (often male) |
| Usual presentation | Marrow failure: fatigue (anemia), infections (neutropenia), bleeding/petechiae (thrombocytopenia); bone pain | Same marrow failure symptoms + more likely mediastinal mass symptoms |
| Key “classic” clue | Bone pain and constitutional symptoms; sometimes LAD/HSM | Cough, dyspnea, SVC syndrome from anterior mediastinal mass |
| Cell of origin | Precursor B lymphoblasts | Precursor T lymphoblasts |
| Immunophenotype | TdT+, CD10+ (CALLA), often CD19+, CD22+ | TdT+, CD3+, often CD7+ |
| Smear/BM | Lymphoblasts (scant cytoplasm, inconspicuous nucleoli) | Same |
| Cytogenetics (high yield) | t(12;21) (ETV6-RUNX1) = good prognosis; hyperdiploidy = good; t(9;22) (BCR-ABL) = worse | Can involve NOTCH1 mutations (often mentioned), but Step commonly tests the mediastinal mass more than specific translocations |
| Key complication | Tumor lysis syndrome with treatment; CNS involvement risk | Same + airway/SVC risk from mass |
| Treatment pearls (Step-level) | Multi-agent chemo; CNS prophylaxis (intrathecal); BCR-ABL+ gets a TKI (e.g., imatinib) | Multi-agent chemo; CNS prophylaxis |
Genetics & prognosis: the “must-know” list
Better prognosis
- t(12;21) (ETV6-RUNX1): very common in pediatric B-ALL
- Hyperdiploidy (more chromosomes): generally favorable
Worse prognosis
- t(9;22) (BCR-ABL, Philadelphia chromosome)
- More common in adults but can occur in ALL
- High-yield treatment add-on: TKI (e.g., imatinib/dasatinib) + chemo
What questions love to ask (classic stems)
1) Marrow failure triad
- Anemia → fatigue, pallor
- Thrombocytopenia → petechiae, mucosal bleeding
- Neutropenia → recurrent infections
2) Bone pain in a child
Marrow expansion from blasts can cause bone pain—a classic “don’t miss ALL” clue.
3) Anterior mediastinal mass = think T-ALL
- Compression symptoms: cough, dyspnea
- SVC syndrome: facial swelling, venous distension
- Mechanism: thymic involvement
Rapid differentiation (ALL vs common look-alikes)
| Disorder | Biggest separator from ALL |
|---|---|
| AML | Auer rods, MPO+, often DIC in APL subtype |
| CLL | Older adults, smudge cells, mature lymphocytes |
| Infectious mononucleosis | Atypical lymphocytes but not blasts; heterophile antibody positivity; clinical mono features |
| ITP | Isolated thrombocytopenia (ALL often causes pancytopenia or multiple cell-line abnormalities) |
Ultra–high-yield test hooks (memorize these)
- TdT+ = lymphoid precursor (ALL and lymphoblastic lymphoma)
- CD10 (CALLA)+ = classic B-ALL
- T-ALL → teen + mediastinal mass
- t(12;21) = good prognosis
- t(9;22) = bad prognosis; add a TKI
- Treat with chemo plus CNS prophylaxis (ALL likes to hide in CNS)