Acute leukaemias are heterogeneous clonal neoplasms of haematopoietic progenitor cells characterized by the accumulation of blast cells in the bone marrow, peripheral blood, and extramedullary sites. They are broadly categorized into Acute Myeloid Leukaemia (AML) and Acute Lymphoblastic Leukaemia (ALL). Rapid diagnosis, precise molecular classification, and risk-adapted therapy—including intensive chemotherapy, targeted agents, and allogeneic haematopoietic stem cell transplantation (allo-HSCT)—are critical for optimizing outcomes. This article provides a structured overview of the current diagnostic framework, risk stratification, and evidence-based management strategies.
1. Introduction & Epidemiology
- Incidence: AML is the most common acute leukaemia in adults (~20,000 cases/year US), with a median age at diagnosis of ~68 years. ALL peaks in early childhood (2–5 years) and again in older adults (>50 years).
- Aetiology: Most cases arise de novo. Risk factors include prior chemotherapy/radiation (therapy-related myeloid neoplasms – t-MN), antecedent haematologic disorders (MDS, MPN), genetic predisposition syndromes (e.g., TP53 germline, Down syndrome), and environmental exposures (benzene, smoking).
2. Classification: The Modern Integrated Approach
The historical FAB morphology-based system has been superseded by the WHO 5th Edition (2022) and International Consensus Classification (ICC 2022). Both emphasize an integrated diagnosis combining morphology, immunophenotype, cytogenetics, and molecular genetics.
A. Acute Myeloid Leukaemia (AML)
Defining Threshold: ≥ 20% blasts in BM/PB (or <20% with specific defining genetic abnormalities).
Key WHO 2022 Defining Categories:
- AML with Defining Genetic Abnormalities (Diagnosis irrespective of blast count):
- PML::RARA (APL, AML-M3), RUNX1::RUNX1T1, CBFB::MYH11, DEK::NUP214, KMT2A rearrangements, NPM1 mutated, CEBPA bZIP in-frame mutated.
- AML with Myelodysplasia-Related Changes (AML-MR): Defined by prior MDS/MPN, MDS-related cytogenetics (e.g., complex karyotype, -7, del(5q)), or multi-lineage dysplasia (≥50% in ≥2 lineages).
- Therapy-Related Myeloid Neoplasms (t-MN): Post-cytotoxic therapy; often TP53 mutated, complex karyotype.
- AML, Not Otherwise Specified (AML-NOS): Defined by lineage (e.g., AML with minimal differentiation, without maturation, with maturation, acute basophilic, myelomonocytic, monocytic, erythroid, megakaryoblastic).
- Myeloid Sarcoma: Extramedullary myeloid tumour.
B. Acute Lymphoblastic Leukaemia (ALL)
Defining Threshold: ≥ 20% lymphoblasts (WHO) or >25% (ICC) in BM.
Lineage Assignment (Immunophenotype Essential):
- B-ALL: CD19+, CD79a+, cytoplasmic CD22+ or CD10+.
- T-ALL: Cytoplasmic CD3+ (earliest), CD7+, CD1a+ (cortical), CD4+/CD8+ (mature).
Key Genetic Subtypes (Defining Entities):
- B-ALL: ETV6::RUNX1 (favourable), BCR::ABL1 (Ph+), KMT2A rearranged (infant, poor), TCF3::PBX1, DUX4 rearranged, MEF2D rearranged, ZNF384 rearranged, PAX5 alterations, IKZF1 deletion (poor prognosis), “Ph-like” (kinase-activated, high risk).
- T-ALL: TLX1/3, TAL1/2, LYL1/LMO2, HOXA cluster, TP53 mutations (adverse).
3. Clinical Presentation
| Feature | AML | ALL |
|---|---|---|
| Onset | Days to weeks (often insidious in elderly) | Days to weeks (often acute/fulminant) |
| Cytopenias | Anaemia, thrombocytopenia (epistaxis, petechiae), neutropenia (fever/infection) | Similar; thrombocytopenia often more severe |
| Leukostasis | WBC > 50–100 x10⁹/L (esp. monocytic/myelomonocytic) | WBC > 100–200 x10⁹/L (T-ALL > B-ALL) |
| Extramedullary | Gingival hyperplasia (monocytic), skin nodules (myeloid sarcoma), CNS rare | CNS involvement common (5-10% at Dx); testicular relapse (sanctuary site); mediastinal mass (T-ALL) |
| Coagulopathy | DIC hallmark of APL (M3) | Rare at presentation |
Emergencies:
- Tumour Lysis Syndrome (TLS): High WBC, bulky disease, high LDH/uric acid. Prophylaxis: Hydration, Allopurinol/Rasburicase.
- Leukostasis/Respiratory Distress: Hydroxyurea for rapid cytoreduction; Leukapheresis indicated for symptomatic hyperleukocytosis (neurological/respiratory) after hydroxyurea initiation. Contraindicated in APL (bleeding risk).
- APL Coagulopathy: Immediate ATRA + supportive transfusion (Cryoprecipitate/FFP/Platelets) targeting Fibrinogen > 1.5–2 g/L, Plt > 30–50 x10⁹/L.
4. Diagnostic Workup (Mandatory Baseline)
| Investigation | Purpose | Critical Details |
|---|---|---|
| FBC + Film | Blast count, dysplasia, Auer rods | Differential for APL (hypergranular promyelocytes) |
| BM Aspirate/Trephine | Morphology (blast %), cellularity, fibrosis | Core biopsy essential if “dry tap” or suspected fibrosis |
| Flow Cytometry (Immunophenotyping) | Lineage assignment (AML vs ALL), MRD baseline | LAIP (Leukaemia-Associated Immunophenotype) definition |
| Cytogenetics (Karyotype/FISH) | Risk stratification, defining abnormalities | 20 metaphases minimum; FISH for PML::RARA, RUNX1::RUNX1T1, BCR::ABL1, KMT2A |
| Molecular Genetics (NGS Panel) | Prognosis, Targetable mutations, MRD targets | NPM1, FLT3-ITD/TKD, IDH1/2, DNMT3A, TP53, ASXL1, RUNX1, CEBPA, KMT2A-PTD, WT1, NRAS/KRAS, PTPN11, JAK2 |
| Lumbar Puncture | CNS assessment | Mandatory in ALL (diagnostic/prophylactic IT chemo); In AML: only if neurological symptoms or WBC > 40-50 (controversial) |
| Organ Function | Fitness for therapy | LFTs, U&Es, Ca²⁺/PO₄/UrIC (TLS), Coagulation, Echo/MUGA (Anthracycline baseline), Viral serology (HIV, Hep B/C, CMV, HSV, VZV) |
| HLA Typing | Donor search | Patient + Siblings immediately for intermediate/adverse risk AML & high-risk ALL |
5. Risk Stratification (Guides Consolidation: Chemo vs. Transplant)
AML (ELN 2022 Risk Classification)
Requires complete molecular + cytogenetic data.
| Risk Group | Defining Features | Post-Remission Strategy |
|---|---|---|
| Favourable | PML::RARA (APL); NPM1 mut (no FLT3-ITD or low allelic ratio <0.5); CEBPA bZIP in-frame mut; RUNX1::RUNX1T1 / CBFB::MYH11 (Core Binding Factor) | Consolidation Chemo (High-dose Ara-C); No allo-HSCT in CR1 (except molecular relapse) |
| Intermediate | NPM1 mut + FLT3-ITD high ratio; FLT3-ITD low ratio (no NPM1); Wild-type NPM1 without adverse markers; KMT2A rearranged (specific partners) | Allo-HSCT in CR1 generally recommended for fit patients (esp. FLT3-ITD high ratio); MRD-guided decisions evolving |
| Adverse | Complex karyotype (≥3 abn); Monosomal karyotype; TP53 mut; FLT3-ITD high ratio (if not intermediate); ASXL1, RUNX1, BCOR, SRSF2, U2AF1, ZRSR2 mut (MR-related); MECOM inv(3); KMT2A rearr (specific); t-MN | Allo-HSCT in CR1 strongly indicated if fit; Clinical trials / Hypomethylating agents + Venetoclax if unfit |
ALL (Adult Risk Stratification – e.g., UKALL14 / NCCN / EWALL)
Based on Age, WBC, Genetics, & MRD Response (Most powerful prognosticator).
| Risk Group | Features | Consolidation |
|---|---|---|
| Standard Risk (SR) | Age 18–40, WBC < 30 (B) / < 100 (T), No adverse genetics, MRD negative (≤10⁻⁴) post-Induction | Chemotherapy only (No transplant in CR1) |
| High Risk (HR) | Age > 40, High WBC, Adverse genetics (BCR::ABL1, KMT2A-r, Ph-like, IKZF1^del, TP53), MRD Positive post-Induction | Allo-HSCT in CR1 standard |
| Ph+ ALL (BCR::ABL1) | Distinct entity | TKI (Imatinib/Dasatinib/Ponatinib) + Chemo → Allo-HSCT in CR1 (if MRD neg, chemo+TKI alone debated) |
6. Management Principles
A. Acute Promyelocytic Leukaemia (APL) – Medical Emergency
- Diagnosis: Clinical suspicion → Start ATRA (All-Trans Retinoic Acid) 45 mg/m²/day IMMEDIATELY while awaiting PML::RARA confirmation.
- Induction: ATRA + Arsenic Trioxide (ATO) is standard of care (non-chemo) for low/intermediate risk (WBC ≤ 10). High risk (WBC > 10): ATRA + ATO + Idarubicin (or AIDA regimen: ATRA + Anthracycline).
- Differentiation Syndrome: Fever, hypotension, pulmonary infiltrates, pleural/pericardial effusions, weight gain. Treat immediately with Dexamethasone 10mg IV q12h. Do not stop ATRA/ATO unless life-threatening.
- Maintenance: ATRA (+/- 6-MP/MTX) x 2 years (standard risk); ATO consolidation cycles (high risk).
B. AML (Non-APL) – “Fit” Patients (Age < 60–70, Fit Elderly)
- Induction (“7+3” Backbone):
- Cytarabine 100–200 mg/m²/day CI Days 1–7 + Anthracycline (Daunorubicin 60–90 mg/m² or Idarubicin 12 mg/m² Days 1–3).
- Targeted Additions:
- FLT3-ITD/TKD: Midostaurin Days 8–21 (RATIFY trial).
- CD33+: Gemtuzumab Ozogamicin (GO) Day 1, 4, 7 (ALFA-0706/UK NCRI AML17) – Caution: VOD/Sinusoidal Obstruction Syndrome risk.
- Response Assessment: Day 14–21 Marrow. MRD (Flow/NGS) at end of Induction (CR/CRi) is prognostic.
- Consolidation:
- Favourable Risk: 3–4 cycles High-Dose Cytarabine (HiDAC) 3g/m² q12h Days 1, 3, 5 (age < 60).
- Intermediate/Adverse Risk: Allo-HSCT in CR1 (Matched Sibling > MUD > Haploidentical/Cord). FLT3-ITD patients: Maintenance Midostaurin/Sorafenib post-transplant (SORMAIN/ADMIRAL data).
- IDH1/2 mutated relapse/refractory: Ivosidenib / Enasidenib (Targeted monotherapy).
C. AML – “Unfit” / Elderly Patients (Age > 70–75 or Comorbidities)
- Venetoclax (BCL-2 inhibitor) + Hypomethylating Agent (Azacitidine/Decitabine) or Low-Dose Cytarabine (LDAC). (VIALE-A, VIALE-C trials).
- Response: Higher CR/CRi rates vs HMA alone; outpatient feasible; infectious vigilance (neutropenia).
- Alternative: HMA monotherapy, LDAC, Glasdegib + LDAC, Clinical Trials.
- CPX-351 (Liposomal Daunorubicin/Cytarabine): Approved for t-AML / AML-MR (secondary AML) in patients 60–75 yrs.
D. ALL (Adults) – Pediatric-Inspired Regimens (e.g., UKALL14, GRAALL, Hyper-CVAD, Linker)
- Phases: Induction → Consolidation/Intensification → Interim Maintenance/Delayed Intensification → Maintenance (2–3 years total).
- Key Components: Multi-agent (Vincristine, Dexamethasone/Prednisolone, Anthracycline, Cyclophosphamide, Cytarabine, Methotrexate, 6-MP, Asparaginase).
- Asparaginase (PEG-Asparaginase/Erwinia): Critical for EFS; monitor toxicity (pancreatitis, thrombosis, coagulopathy, hypersensitivity).
- CNS Prophylaxis: Mandatory Intrathecal Chemotherapy (IT MTX/Ara-C/Hydrocortisone) throughout protocol. Cranial irradiation reserved for CNS3 disease or high-risk T-ALL.
- Ph+ ALL: Add TKI (Dasatinib/Ponatinib preferred for CNS penetration) from Day 1 Induction.
- Ph-like ALL: Trial of TKI (Dasatinib/Ruxolitinib) + Chemo if kinase pathway activated (e.g., CRLF2/JAK2, ABL-class fusions).
E. Relapsed/Refractory (R/R) Disease
- AML: Re-induction (FLAG-IDA, CLAG-M, MEC) → Bridge to Allo-HSCT. Targeted agents: Gilteritinib (FLT3), Ivosidenib/Enasidenib (IDH1/2), Magrolimab (CD47 – investigational), Menin inhibitors (KMT2A-r, NPM1 – clinical trials).
- ALL: Blinatumomab (BiTE, CD3xCD19) → MRD negativity → Allo-HSCT. Inotuzumab Ozogamicin (Anti-CD22 ADC). CAR-T Therapy (Tisagenlecleucel, Brexucabtagene autoleucel) approved for R/R B-ALL (up to age 25–26 for Tisa, Adult for Brexu). TECVAYLI (Teclistamab) / Talquetamab (Bispecifics) emerging.
7. Supportive Care Essentials
- Transfusion Thresholds: Hb < 70–80 g/L (symptomatic); Plt < 10 x10⁹/L (prophylactic), < 20 (fever/sepsis), < 50 (active bleed/invasive proc), < 100 (CNS bleed/APL).
- Infection Prophylaxis:
- Antibacterial: Fluoroquinolone (Ciprofloxacin/Levofloxacin) during prolonged neutropenia (ANC < 0.5).
- Antifungal: Posaconazole (AML induction/consolidation, GVHD prophylaxis) or Voriconazole/Isavuconazole.
- Antiviral: Aciclovir/Valaciclovir (HSV/VZV prophylaxis); Monitor CMV/EBV/BK virus PCR post-transplant.
- G-CSF: Primary prophylaxis if febrile neutropenia risk > 20% (standard in AML induction/consolidation); Secondary prophylaxis if prior FN.
- TLS Prophylaxis: Rasburicase (high risk), Allopurinol (intermediate), Aggressive hydration.
- Fertility Preservation: Sperm banking / Oocyte/Embryo cryopreservation before treatment initiation (discuss with all reproductive-age patients).
8. Measurable Residual Disease (MRD) – The Paradigm Shift
- Methods: Multiparameter Flow Cytometry (MFC; sensitivity 10⁻⁴–10⁻⁵), RT-qPCR (Fusion transcripts, NPM1, WT1), NGS (Mutation clearance, sensitivity 10⁻⁵–10⁻⁶).
- Clinical Utility:
- Prognostic: MRD negativity = better OS/DFS.
- Therapeutic Decision Making:
- AML: MRD+ post-consolidation → Stronger indication for Allo-HSCT; MRD- favourable risk → Omit transplant.
- ALL: MRD status at end of Induction (Day 29) and Consolidation defines risk group (SR vs HR) and transplant indication.
- Post-Transplant: Molecular relapse (rising NPM1, RUNX1::RUNX1T1, BCR::ABL1) → Pre-emptive intervention (DLI, Azacitidine, TKI restart, targeted therapy).
9. Prognosis & Survivorship
- AML: 5-yr OS ~ 30% overall (Highly age/risk dependent: Favourable ~60-70%, Adverse ~10-20%). Cure plateau reached for favourable risk.
- ALL: 5-yr OS Adults ~ 40-50% (Ph+ improved to 50-60% with TKI+Transplant; Ph- SR ~60-70%). Pediatric ALL > 90%.
- Late Effects: Cardiomyopathy (Anthracyclines), Endocrinopathy (Hypothyroidism, Hypogonadism, Metabolic syndrome), Neurocognitive deficits (Cranial RT/High-dose MTX), Secondary Malignancies (t-MN, solid tumours), Chronic GVHD (Post-transplant), Psychosocial/Financial toxicity.
- Survivorship Care Plan: Risk-based screening (Echo q 2-5 yrs, TFTs, Lipids, DEXA, Cancer screening, Vaccination schedules).
10. Key Takeaways for the Clinician
- Time is Tissue: Suspected APL = Start ATRA immediately (do not wait for genetics). Suspected ALL/AML with high WBC = Hydroxyurea + TLS prophylaxis + Urgent Haematology Referral.
- Genetics Drive Therapy: Treatment cannot be optimized without Karyotype + FISH + NGS Panel. Send samples before starting steroids (lymphoid) or hydroxyurea (myeloid) if possible.
- MRD is the New Standard: Response assessment is no longer just morphology. Flow/PCR/NGS MRD dictates transplant decisions and predicts relapse months early.
- Age is not a Sole Barrier: “Fit” vs “Unfit” assessment (Geriatric Assessment, HCT-CI) guides Intensive vs. Lower-Intensity (Venetoclax-based) strategies.
- Transplant Referral Early: HLA typing at diagnosis for all intermediate/adverse AML and high-risk ALL. Do not wait for remission confirmation.
- Clinical Trials: The standard of care evolves rapidly (Menin inhibitors, Bispecifics, Novel CAR-Ts, Magrolimab). Enrolment should be discussed at every decision point.
References & Key Guidelines
- WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues, 5th Ed (2022).
- International Consensus Classification (ICC) of Myeloid/Lymphoid Neoplasms (Blood 2022).
- ELN 2022 Risk Stratification for AML (Döhner et al., Blood 2022).
- NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®): Acute Myeloid Leukaemia / Acute Lymphoblastic Leukaemia (V2.2024).
- EORTC / GIMEMA / UKALL / HOVON / MDACC Protocols.
- EBMT/ESH Guidelines for Allo-HSCT Indications (2023).
- Key Trials: RATIFY (Midostaurin), VIALE-A/C (Venetoclax), QUAZAR (CC-486 Maintenance), SORMAIN (Sorafenib maintenance), ALFA-0706 (GO), TOWER/CASSIOPEIA (Blinatumomab/InO), ZUMA-3/ELIANA (CAR-T).
Disclaimer: This article is for educational purposes only and does not constitute individual medical advice. Treatment protocols vary by institution, geography, drug availability, and patient-specific factors. Always consult local guidelines and a haematology specialist.