Acute Leukaemia (AML & ALL, including APL)

Meet the patient

A 38-year-old woman arrives in A&E with three weeks of gum bleeding, heavy periods, and a sore throat that turned into a fever overnight. She is pale, her gums are swollen and oozing, and there are petechiae over her ankles. Bloods: Hb 64, platelets 18, WBC 88, and the lab phones to say the film shows blasts with bundles of Auer rods.^[2]

The registrar wants to book induction chemotherapy for AML. The consultant's first move is the opposite of booking: send a coagulation screen now, and if the fibrinogen is low with a high D-dimer, start ATRA before the cytogenetics come back. Because this woman has acute promyelocytic leukaemia, and the way APL patients die is intracranial haemorrhage in the first days — before the t(15;17) result ever arrives.^[2][10]

What acute leukaemia is — blasts, and a 20 percent line

Acute leukaemia is a clonal haematological malignancy arising from a single haematopoietic progenitor that has acquired two cardinal defects — a block in differentiation (so cells accumulate as immature blasts rather than maturing) and uncontrolled proliferation (so the clone expands exponentially). The expanding blast mass effaces the marrow and spills into the blood, producing the clinical syndrome of marrow failure.^[1]

The diagnostic cornerstone is the blast percentage: acute leukaemia is defined by marrow (or blood) blasts of at least 20 percent of nucleated cells. This threshold separates it from myelodysplastic syndrome (blasts under 20 percent, with dysplasia) and from chronic leukaemia (dominated by mature-appearing cells). Two defining-genetic exceptions override the 20 percent rule: t(15;17) PML-RARA (APL) is acute leukaemia at any blast count, and other AML-defining genetic abnormalities (t(8;21), inv(16)) qualify as AML even with 10 to 19 percent blasts under the WHO 2022 and International Consensus Classification.^[1]

Acute leukaemia then divides by lineage of the blast into acute myeloid leukaemia (AML) — the commonest acute leukaemia of adults — and acute lymphoblastic leukaemia (ALL) — the commonest childhood cancer. A third axis is biological: de novo, secondary (from antecedent MDS or myeloid neoplasm), and therapy-related (after prior cytotoxic chemo or radiotherapy).^[1]

Classification — FAB morphology, then genetics that outrank the 20 percent rule

Acute leukaemia is classified by lineage (myeloid vs lymphoid), morphology (the FAB system), and — for AML — defining genetic abnormalities (WHO 2022 and International Consensus Classification). The modern standard is genetic, because cytogenetic or molecular subtype drives prognosis and treatment far more powerfully than morphology.^[1]

FAB classification of AML (M0 to M7)

The French-American-British morphological classification divides AML by blast morphology into M0 to M7. The exam-critical fact is that M3 (acute promyelocytic leukaemia, APL) is a standalone clinical emergency.^[1]

WHO 2022 and International Consensus Classification of AML

The WHO 2022 and the ICC reframe AML around genetic drivers rather than morphology. The exam value is to recognise that defining genetic abnormalities outrank the 20 percent rule and that the ELN 2022 genetic risk groups (favourable, intermediate, adverse) drive the treatment decision — consolidate with chemotherapy versus proceed to allogeneic stem-cell transplant.^[1]

Classification of ALL

ALL is classified by immunophenotype (B-ALL versus T-ALL, with sub-stages of maturation) and by cytogenetics or molecular lesions, of which the most important is the Philadelphia chromosome t(9;22)(q34;q11.2) BCR-ABL1, present in about 3 percent of children but around 25 percent of adults (rising with age).^[1]

Epidemiology and risk factors — mirror-image age curves

Acute leukaemia is the commonest cancer of childhood, and AML is the commonest acute leukaemia of adults. The two diseases have mirror-image age distributions:^[1]

Acquired risk factors for AML: prior cytotoxic chemotherapy or radiotherapy (therapy-related AML), antecedent MDS or myeloproliferative neoplasm (secondary AML), benzene and petrochemical or solvent exposure, smoking, and ionising radiation. Inherited or germline risk factors: Down syndrome (10 to 20-fold risk of AML — and the unique transient abnormal myelopoiesis, TAM, of the neonate), Fanconi anaemia, Bloom syndrome, ataxia-telangiectasia, Li-Fraumeni syndrome, Kostmann or severe congenital neutropenia, and Shwachman-Diamond syndrome.^[1]

Therapy-related AML (t-AML) deserves its own recognition. Two drug classes predispose, with characteristic latency and cytogenetics: alkylating agents (melphalan, cyclophosphamide, chlorambucil) and ionising radiation give a myelodysplasia-like picture after 5 to 7 years, typically with monosomy 5 or 7 or complex karyotype (adverse); and topoisomerase-II inhibitors (etoposide, teniposide, doxorubicin, mitoxantrone) give shorter latency (1 to 3 years), often with balanced translocations involving KMT2A (11q23) or RUNX1 (t(8;21)). t-AML carries a poor prognosis.^[1]

Pathophysiology — the two-hit model, then four emergencies

The malignant cell of acute leukaemia is the blast — an immature precursor trapped at an early differentiation stage by a differentiation block, while retaining the capacity for self-renewal and uncontrolled proliferation. Two cooperating classes of mutation drive this, formalised as the two-hit model: class I mutations activate proliferative or survival signalling (FLT3, RAS, JAK2) and class II mutations impair differentiation (PML-RARA, RUNX1-RUNX1T1, NPM1, CEBPA). A clinical acute leukaemia usually carries one of each.^[1]

As blasts expand they physically displace and paralyse normal haematopoiesis, producing the triad of marow failure:^[1]

• Anaemia — loss of erythroid precursors to fatigue, pallor, dyspnoea, cardiac decompensation.
• Infection — loss of functional neutrophils (neutropenia) to bacterial, fungal and reactivation infections.
• Bleeding — loss of platelets (thrombocytopenia), compounded in APL by DIC to petechiae, gum bleeding, fundal haemorrhage, intracranial bleed.^[1]

Molecular pathogenesis of APL — the curable emergency

Acute promyelocytic leukaemia (APL, FAB M3) is the archetype of mechanism-defined therapy. The t(15;17)(q24.1;q21.2) translocation fuses the PML gene on chromosome 15 with the retinoic-acid receptor alpha (RARA) gene on chromosome 17, generating the PML-RARA fusion oncoprotein. This fusion protein dominantly represses transcription of genes needed for myeloid differentiation (by recruiting the N-CoR or SMRT or histone-deacetylase co-repressor complex) so the cell is arrested at the promyelocyte stage. At pharmacological (not physiological) concentrations, all-trans retinoic acid (ATRA) binds the fusion protein, releases the co-repressor and restores differentiation — the blasts mature into terminal neutrophils and die.^[2]

The APL coagulopathy is a DIC-like state driven by procoagulant tissue factor and annexin II released from the abnormal promyelocyte granules, plus enhanced fibrinolysis (annexin II upregulates t-PA). The result is prolonged PT and aPTT, low fibrinogen, high D-dimer and thrombocytopenia — with simultaneous bleeding and thrombosis. This coagulopathy is why APL patients die of intracranial haemorrhage in the first days, and why ATRA must be started on suspicion and fibrinogen and platelets aggressively corrected.^[2][10]

Mechanism of tumour lysis syndrome (TLS)

Rapid lysis of a large tumour mass (high-burden AML with high WBC, ALL — especially Burkitt-like or T-ALL, or any proliferative leukaemia at treatment onset) releases intracellular contents faster than the body can excrete them: potassium (hyperkalaemia to cardiac arrhythmia), phosphate (hyperphosphataemia, which precipitates with calcium to hypocalcaemia and nephrocalcinosis), and nucleic acids metabolised to uric acid (urate crystallises in the renal tubules to acute urate nephropathy and AKI). The AKI then worsens hyperkalaemia and hyperphosphataemia — a vicious circle.^[7]

Mechanism of leucostasis (hyperleukocytosis)

When the white-cell count is very high (classically over 100 times 10^9 per L in AML, over 400 in ALL — the threshold differs because myeloblasts are larger and stickier), the blasts form leukocyte aggregates or thrombi in the microvasculature, especially the cerebral (confusion, visual disturbance, stroke, intracranial haemorrhage) and pulmonary (dyspnoea, hypoxia, diffuse infiltrates) beds. Blasts also express adhesion molecules and consume endothelial nitric oxide. The risk is compounded by anaemia and by APL (bleeding). Cytoreduction is urgent.^[1]

Recurrent AML mutations that drive biology and prognosis

The ELN 2022 risk stratification rests on the cytogenetic or molecular profile. The recurrent mutations the examiner expects:^[1]

Clinical presentation — marrow failure, infiltration, and four emergencies

The clinical syndrome is dominated by marrow failure, modulated by tissue infiltration (extramedullary disease), leucostasis, DIC (APL) and tumour lysis. Most patients present over days to weeks of progressive symptoms.^[1]

The marrow-failure triad:^[1]

• Anaemia — fatigue, pallor, dyspnoea, exertional limitation, angina or cardiac failure in older patients; on examination, conjunctival or palmar pallor.
• Infection or neutropenia — fever, mucositis, pneumonia, cellulitis, perianal infection, septicaemia; opportunistic organisms (Pseudomonas, gram-negatives, Staphylococcus, Candida, Aspergillus, reactivation of herpes). Febrile neutropenia is a medical emergency.
• Bleeding or thrombocytopenia — petechiae, purpura, epistaxis, gum bleeding, menorrhagia, haematuria, fundal haemorrhage, and catastrophic intracranial bleed. In APL the bleeding is amplified by DIC.^[1]

Tissue infiltration or extramedullary disease:^[1]

APL presentation: mucocutaneous bleeding is dominant and often the first symptom — petechiae, gum bleeding, epistaxis, GI or GU bleeding, haematuria, menorrhagia, intracranial haemorrhage; bruising disproportionate to platelet count (because DIC). Low fibrinogen, prolonged PT and aPTT, raised D-dimer. APL patients are the ones who die before reaching the ward: any new diagnosis of acute leukaemia with bleeding should be treated as APL until proven otherwise.^[2][10]

Hyperleukocytosis or leucostasis: confusion, somnolence, visual disturbance (retinal vein distension, haemorrhage), dyspnoea, hypoxia, and priapism. A WBC over 100 times 10^9 per L in AML is a hyperleukocytosis emergency regardless of symptoms.^[1]

Tumour lysis at presentation: oliguria, AKI, nausea or vomiting, cardiac arrhythmia or sudden death from hyperkalaemia, tetany or seizures from hypocalcaemia, lethargy. Most often emerges within hours to days of starting therapy in a high-burden leukaemia.^[7]

Atypical presentations: elderly — fatigue, anorexia, "off legs", delirium attributed to infection; cytopenias dismissed as "old age". Pregnancy — fatigue and anaemia of pregnancy mask the disease.^[1]

Differential diagnosis — acute leukaemia versus its mimics

The hardest practical distinction is acute leukaemia versus a severe leukaemoid reaction. In overwhelming infection (especially in children) the white count can exceed 50 times 10^9 per L with circulating immature forms. The decisive features pointing to leukaemia are: a clonal blast population (flow cytometry), Auer rods (pathognomonic for AML), persistent cytopenias (a leukaemoid reaction does not cause them), maturation arrest, no obvious focus of infection, and cytogenetic or molecular abnormality. A leucocyte alkaline phosphatase (LAP) score is high in leukaemoid reaction and low in CML.^[1]

Acute leukaemia versus aplastic anaemia — both cause pancytopenia. In aplastic anaemia the marrow is hypocellular (empty) with no clonal blasts, there is no hepatosplenomegaly or lymphadenopathy, and the peripheral blood shows no blasts. In acute leukaemia the marrow is hypercellular with sheets of blasts. The distinction is made on bone-marrow aspirate and trephine biopsy.^[1]

Non-malignant causes of pancytopenia to exclude: megaloblastic anaemia (B12 or folate deficiency), severe infection (visceral leishmaniasis or kala-azar, miliary TB, HIV, viral hepatitis), drugs (chemotherapy, clozapine, antithyroid drugs, linezolid), hypersplenism or portal hypertension, systemic lupus erythematosus, paroxysmal nocturnal haemoglobinuria (PNH), and bone-marrow infiltration (metastatic carcinoma, miliary TB).^[1]

Clinical and bedside assessment

A focused examination in suspected acute leukaemia looks for evidence of marrow failure, tissue infiltration, and the four emergencies (DIC or bleeding, leucostasis, tumour lysis, febrile neutropenia). Examine systematically:^[1]

• General — pallor (anaemia), petechiae and purpura (especially over ankles, pressure points, buccal mucosa — thrombocytopenia or DIC), bruising disproportionate to trauma, jaundice (haemolysis, drug, infection).
• Mouth — gum hypertrophy (monocytic AML, M4 or M5), mucositis (neutropenia), oral candidiasis, gingival bleeding, aphthae.
• Nodes — cervical, supraclavicular, axillary, epitrochlear, inguinal (lymphadenopathy more in ALL).
• Abdomen — hepatosplenomegaly (infiltration; marked in monocytic AML and ALL; massive in CML), tenderness (typhlitis in neutropenia).
• Skin — chloroma (myeloid sarcoma), leukaemia cutis, infection foci (cellulitis, line sites, perianal).
• Eyes — fundoscopy for retinal haemorrhage (thrombocytopenia, leucostasis — Roth spots with infection).
• Chest — pneumonia, mediastinal mass (T-ALL — stridor or SVC syndrome).
• CNS — cranial-nerve palsy (especially facial nerve) = CNS leukaemia, meningism, confusion (leucostasis, intracranial bleed, hypocalcaemia).
• Genitalia (boys) — testicular enlargement (B-ALL sanctuary site).
• Infection foci — perianal (perianal abscess in neutropenia), central line site, skin, chest, urine, meninges.^[1]

Bedside observations that demand escalation (a haematological emergency):^[1]

• Fever over 38.3C (single) or over 38.0C sustained over one hour in a neutropenic patient = febrile neutropenia — empirical anti-pseudomonal beta-lactam within one hour (door-to-needle).
• Bleeding with prolonged PT or aPTT and low fibrinogen (suspected APL or DIC) — start ATRA immediately, correct fibrinogen and platelets.
• Confusion, visual change or dyspnoea with WBC over 100 (leucostasis) — leucopheresis, hydroxycarbamide, urgent cytoreduction.
• Oliguria with hyperkalaemia or hyperphosphataemia (tumour lysis) — rasburicase, cardiac monitoring, renal or nephrology.^[1]

Febrile neutropenia is an emergency because the neutropenic patient cannot localise or contain infection: a small focus becomes septicaemia within hours. Neutropenia is defined as ANC under 0.5 times 10^9 per L (or under 1.0 and falling); fever is over 38.3C single or over 38.0C sustained over one hour. The IDSA principle is immediate empirical broad-spectrum antibiotic therapy covering both gram-positive and gram-negative pathogens, after blood cultures but before their results.^[9]

Investigations — film suggests, flow and genetics decide

The diagnosis rests on peripheral blood and bone marrow, integrated with flow cytometry, cytogenetics and molecular testing. The diagnostic standard is bone-marrow aspirate plus trephine biopsy.^[1]

First-line investigations:^[1]

• Full blood count — anaemia, thrombocytopenia, neutropenia; WBC high, normal or low (about 15 percent present with leukopenia — do not be reassured by a normal or low WBC).
• Peripheral blood film — blasts (large nucleus, high nuclear-to-cytoplasmic ratio, prominent nucleoli, scant agranular cytoplasm for lymphoblasts; granules for myeloblasts), Auer rods (needle-shaped azurophilic inclusions — pathognomonic of AML; bundles = faggot cells in APL or M3). In APL the blasts are abnormal promyelocytes with heavy granulation and multiple Auer rods.
• Coagulation — PT, aPTT, fibrinogen, D-dimer; in APL expect prolonged PT and aPTT, low fibrinogen, high D-dimer (DIC).
• Biochemistry — U&E and creatinine (baseline; AKI from TLS, infiltration, sepsis), urate (high in TLS), LDH (tumour burden, prognostic in ALL), calcium and phosphate (hypocalcaemia or hyperphosphataemia in TLS), LFTs, glucose.
• Group and screen or crossmatch — transfusion support will be needed.
• Viral serology — HIV, hepatitis B and C (affects treatment choice and rituximab or TBI risk); EBV or CMV status in transplant candidates.^[1]

Bone marrow: diagnostic criteria. The diagnostic standard is a bone-marrow aspirate plus trephine biopsy. Acute leukaemia requires marrow (or blood) blasts at least 20 percent (or a defining genetic lesion such as PML-RARA, RUNX1-RUNX1T1, CBFB-MYH11). The aspirate provides morphology and material for flow cytometry, cytogenetics (karyotype, FISH) and molecular testing (PCR or NGS); the trephine biopsy provides cellularity (hypercellular, packed marrow in acute leukaemia), architecture and is essential when the aspirate is a "dry tap".^[1]

Flow cytometry (immunophenotyping) determines lineage and is essential. The key markers:^[1]

Cytogenetics and molecular testing — the ELN 2022 risk groups. Conventional karyotype and FISH identify the recurring translocations; molecular testing (PCR, NGS) for FLT3 (ITD and TKD), NPM1, CEBPA, RUNX1, TP53, IDH1 or IDH2, KIT refines prognosis and matches the patient to a targeted agent (midostaurin or gilteritinib for FLT3, venetoclax, IDH inhibitors). The ELN 2022 risk groups (reproduced in principle):^[1]

BCR-ABL1 (Philadelphia chromosome) testing in ALL is mandatory for every adult with newly diagnosed ALL (and considered in children). The t(9;22) fusion drives constitutive ABL1 tyrosine-kinase activity; outcomes in Ph-positive ALL have improved with the use of tyrosine kinase inhibitors. Detected by karyotype, FISH or RT-PCR.^[13][14]

Laboratory criteria of tumour lysis syndrome (TLS). TLS is defined clinically (Cairo-Bishop classification). Laboratory TLS requires two or more of the four classic metabolic derangements — hyperuricaemia, hyperkalaemia, hyperphosphataemia and hypocalcaemia — appearing around the start of cytotoxic therapy. Clinical TLS is laboratory TLS plus clinical toxicity: renal insufficiency or acute kidney injury, cardiac arrhythmias, seizures, neurological complications or sudden death. The incidence is highest in tumours with high proliferative rates and high tumour burden, such as acute lymphoblastic leukaemia and Burkitt lymphoma.^[7][8]

DIC investigations (especially APL): expect the consumptive pattern — PT and aPTT prolonged, fibrinogen low, raised fibrin-related markers or D-dimer, platelets low, with schistocytes on the film. The diagnosis is made with the ISTH scoring system for overt DIC, which combines simple laboratory criteria (platelet count, fibrin-related marker, fibrinogen, prothrombin time) with the presence of an underlying disorder known to trigger DIC — and APL is a textbook trigger.^[16][10]

Lumbar puncture in ALL is performed at diagnosis in patients at risk of CNS disease (high-risk B-ALL, all T-ALL, CNS symptoms) and as part of CNS-directed intrathecal therapy throughout treatment. It looks for leukaemic blasts in the CSF (CNS disease). In AML an LP is reserved for symptoms or high-risk monocytic disease. A platelet count over 50 times 10^9 per L is required before LP; LP is avoided if the patient is hyperleukocytotic or leucostatic because of intracranial-bleed risk.^[13]

Baseline supportive workup before treatment: ECG and echocardiogram (anthracycline cardiotoxicity — cumulative dose), hepatitis B (surface antigen and core antibody — chemotherapy or rituximab reactivates HBV) and hepatitis C and HIV, pregnancy test in women of childbearing age, fertility counselling and sperm or oocyte cryopreservation before gonadotoxic chemo, tissue typing of siblings if allogeneic transplant is anticipated, and dental review before mucositis.^[1]

Management — resuscitation (treat the four emergencies first)

Treat the presenting haemato-oncological emergencies first and set up supportive care, then start definitive chemotherapy. The resuscitation priorities in suspected or confirmed acute leukaemia are: (1) febrile neutropenia, (2) tumour lysis syndrome, (3) leucostasis, (4) APL coagulopathy, and (5) general supportive care (transfusion, hydration, antimicrobial prophylaxis).^[1]

Febrile neutropenia

Empirical broad-spectrum antibiotics immediately — after blood cultures (peripheral and from any central line) but before results — covering both gram-positive and gram-negative pathogens. Standard regimens:^[9]

• An anti-pseudomonal beta-lactam — for example piperacillin-tazobactam (first-line in most units), or
• A carbapenem such as meropenem (if prior resistant organism, septic shock, or ESBL risk), or
• An anti-pseudomonal cephalosporin such as ceftazidime (alternative). Exact dosing is unit protocol — the non-negotiable is speed and breadth.^[9]

Vancomycin (or teicoplanin) is added for suspected gram-positive complications — line infection, severe mucositis, or haemodynamic instability. G-CSF is considered in high-risk neutropenia to shorten the neutropenic phase. If fever persists, reassess for invasive fungal infection (Aspergillus — high-resolution CT thorax, galactomannan): the IDSA guideline frames the choice between empirical and preemptive antifungal therapy.^[9]

Tumour lysis syndrome — prophylaxis and treatment

Begin before the first cytotoxic dose in every high-risk patient (proliferative or high-WBC AML, ALL with high burden, Burkitt-like, LDH markedly raised, pre-existing AKI, urate high). The international TLS consensus panel assigns low, intermediate and high risk to guide how aggressive prophylaxis needs to be:^[8]

• Aggressive intravenous hydration and diuresis — the mainstay of prophylaxis, with vigilant monitoring of electrolyte abnormalities.
• Allopurinol prophylaxis — for lower-risk patients; a xanthine-oxidase inhibitor that prevents new uric-acid formation but does not clear urate that is already there.
• Rasburicase (recombinant urate oxidase) — for high tumour burden or established TLS; it breaks down existing uric acid, and in pooled adult data over 93 percent of patients achieved normalised serum uric acid levels. Urine alkalinisation remains controversial and is no longer routine.^[7][18]

Established TLS treatment: aggressive hydration, rasburicase, treat hyperkalaemia (calcium gluconate for cardioprotection, insulin-dextrose, salbutamol, potassium binders), hypocalcaemia treated only if symptomatic, renal support or haemodialysis for refractory hyperkalaemia, AKI, fluid overload.^[7]

Leucostasis or hyperleukocytosis

Symptomatic leucostasis or hyperleukocytosis (classically a white-cell count over 100 times 10^9 per L in acute leukaemia) demands urgent cytoreduction:^[6]

• Leucopheresis (mechanical white-cell removal) and/or hydroxycarbamide (hydroxyurea) — the two standard cytoreductive measures; the main goal is to reduce the white-cell count before starting induction chemotherapy.
• Aggressive management of concurrent complications — tumour lysis and DIC frequently accompany hyperleukocytosis and must be treated in parallel.
• Start definitive chemotherapy urgently — characterising the leukaemia and beginning tailored definitive treatment is the parallel priority, not an afterthought.^[6]

Suspected APL — the suspicion-based emergency

Any new diagnosis of acute leukaemia with bleeding or with morphological features of M3 (abnormal promyelocytes, heavy granulation, Auer rods or faggot cells) is APL until proven otherwise. Start management before cytogenetic confirmation:^[2][10]

• Start ATRA (all-trans retinoic acid, tretinoin) immediately on suspicion — the classic induction dose is 45 mg per m2 per day orally (the dose at which differentiation therapy was first shown to work: 9 of the first 11 treated APL patients entered complete remission). Do NOT wait for the t(15;17) result — early death before and during induction therapy remains the greatest challenge in APL.
• Aggressively correct the coagulopathy — the ELN APL panel gives specific recommendations for the APL bleeding disorder, including supportive correction with fibrinogen replacement (cryoprecipitate or fibrinogen concentrate), platelets and plasma, with repeated coagulation testing until stable.
• Avoid invasive procedures (central lines placed carefully, no intramuscular injections, avoid unnecessary arterial puncture).
• Refer urgently to a haematology centre. Once PML-RARA is confirmed, add arsenic trioxide — in low-to-intermediate-risk APL (white-cell count up to 10 times 10^9 per L), ATRA plus arsenic trioxide achieved 2-year event-free survival of 97 percent versus 86 percent against ATRA plus chemotherapy.^[11][10][2]

Management — definitive and stepwise

Definitive therapy is lineage- and risk-adapted and is delivered by a specialist haemato-oncology unit. The regimens below are the high-yield core for the MBBS exam — know the acronym expansion, agents, key doses and the rationale.^[1]

AML induction — '7+3'

^[4]

The "7+3" regimen gives cytarabine as a 7-day continuous infusion plus an anthracycline (daunorubicin or idarubicin) for 3 days. Response is assessed at day 14 (marrow cellularity or apoptosis) and day 28 (remission status). Complete remission (CR) is defined as marrow blasts below 5 percent, neutrophils over 1.0 times 10^9 per L, platelets over 100 times 10^9 per L, no extramedullary disease, and transfusion independence. About 60 to 80 percent of younger adults achieve CR with one or two cycles.^[1]

Consolidation follows CR. Favourable-risk AML (CBF, NPM1 without FLT3-ITD) is consolidated with high-dose cytarabine — the same consolidation backbone used in the midostaurin trial. Intermediate- and adverse-risk AML proceeds to allogeneic haematopoietic stem-cell transplant (allo-HSCT) in first CR if a donor is available and the patient is fit — the ELN 2022 recommendations make post-remission therapy risk-adapted. Measurable (minimal) residual disease (MRD) positivity after induction is a strong trigger for transplant or trial therapy.^[4][1]

Midostaurin (an oral multitargeted kinase inhibitor active against FLT3) is added to standard induction (daunorubicin plus cytarabine) and high-dose cytarabine consolidation, followed by maintenance, for FLT3-mutated AML — the landmark phase 3 trial showed a hazard ratio for death of 0.78 and for event or death of 0.78, with benefit across FLT3-ITD (high and low allelic ratio) and TKD subtypes.^[4]

AML — older or unfit patient: venetoclax plus azacitidine

Patients over about 75 years, or with poor performance status or significant comorbidity, are unfit for intensive 7+3. The standard is lower-intensity therapy with azacitidine plus venetoclax:^[3]

• Azacitidine 75 mg per m2 per day subcutaneously or intravenously on days 1 through 7 of each 28-day cycle (hypomethylating agent).
• Venetoclax — a BCL-2 inhibitor — orally once daily at a target dose of 400 mg in 28-day cycles.^[3]

The VIALE-A trial established this combination: median overall survival 14.7 months (venetoclax plus azacitidine) versus 9.6 months (azacitidine plus placebo), with a composite remission rate of about 66 percent versus 28 percent — transforming the outlook of unfit AML.^[3]

Acute promyelocytic leukaemia — ATRA plus arsenic trioxide

APL is treated by differentiation therapy, which has made it the most curable acute leukaemia (2-year event-free survival of 97 percent with ATRA plus arsenic in low-to-intermediate-risk disease):^[2]

^{[11] [2]}

Risk stratification by presenting WBC: non-high-risk (WBC up to 10 times 10^9 per L) = ATRA plus ATO (chemotherapy-free); high-risk (WBC over 10 times 10^9 per L) = ATRA plus ATO plus chemotherapy (idarubicin, the "AIDA"-style addition) and CNS prophylaxis. The APL0406 trial (Lo-Coco) showed ATRA plus arsenic was superior to ATRA plus chemotherapy in non-high-risk APL, sparing patients chemotherapy toxicity.^[2]

ALL — multi-agent induction with CNS prophylaxis

ALL is treated with paediatric-inspired multi-agent chemotherapy in stages — induction, consolidation, CNS-directed therapy, maintenance — over about 2 to 3 years. The backbone of therapy remains multi-agent chemotherapy with vincristine, corticosteroids and an anthracycline, with allogeneic stem-cell transplantation for eligible candidates.^[13]

Induction (about 4 weeks) — the backbone agents:^[13]

• Vincristine — the vinca alkaloid given weekly through every ALL induction regimen.
• Corticosteroid — prednisolone or dexamethasone daily through induction.
• Asparaginase — the third backbone agent of paediatric-inspired regimens (watch hypersensitivity, pancreatitis, thrombosis, hyperglycaemia, low fibrinogen).
• Anthracycline — added in higher-risk or adult regimens.^[13]

CNS-directed intrathecal therapy is non-negotiable throughout ALL treatment: age-adjusted intrathecal chemotherapy (methotrexate, often with cytarabine and hydrocortisone as "triple intrathecal"). Cranial irradiation has been progressively replaced by systemic and intrathecal chemotherapy. The CNS is a sanctuary site that systemic therapy reaches poorly.^[13]

Consolidation or intensification uses cycles of high-dose methotrexate, cytarabine, cyclophosphamide, asparaginase and other agents. Maintenance with daily 6-mercaptopurine and weekly oral methotrexate for 2 to 3 years sustains remission in B-ALL. Allogeneic stem-cell transplant is offered for high-risk ALL (Ph+ in some protocols, MRD-positive, hypodiploid, KMT2A-rearranged, induction failure, relapse).^[13]

Targeted or biological therapy in ALL

Tyrosine-kinase inhibitors have transformed Ph+ ALL — outcomes in Ph-positive ALL have improved with their use. The newest frontline strategy is chemotherapy-free: dasatinib plus glucocorticoids followed by blinatumomab, which achieved complete remission in 98 percent of patients and 95 percent overall survival at a median follow-up of 18 months in adults with newly diagnosed disease.^[14]

Blinatumomab — a bispecific T-cell engager (BiTE) antibody linking CD3 (T cell) to CD19 (B-ALL blast) — brings T cells into contact with leukaemic B cells and induces their lysis; used for MRD-positive and relapsed or refractory B-ALL and increasingly frontline in high-risk disease.^[13][14]

CAR-T cell therapy (tisagenlecleucel) — the patient's own T cells are genetically engineered to express a chimeric antigen receptor against CD19 and reinfused — produces durable remissions in relapsed or refractory B-ALL in children and young adults (ELIANA). Watch for cytokine-release syndrome (fever, hypotension — tocilizumab, steroids) and immune-effector-cell-associated neurotoxicity syndrome (ICANS).^[5]

Supportive care throughout treatment

^[9]

Specific subtypes and scenarios

• Acute promyelocytic leukaemia (APL, M3) — t(15;17) PML-RARA, DIC, the ATRA plus arsenic chemotherapy-sparing strategy, curable in the great majority of non-high-risk disease. The defining management pearl: start ATRA on suspicion, before genetic confirmation.^[2][10]
• Core-binding-factor AML — t(8;21) RUNX1-RUNX1T1 and inv(16) or t(16;16) CBFB-MYH11, the favourable-risk cytogenetic group; treated with intensive chemotherapy plus high-dose cytarabine consolidation, with excellent CR rates; allogeneic transplant reserved for relapse.^[1]
• Philadelphia-chromosome-positive ALL (Ph+ ALL) — once the worst prognosis adult ALL; transformed by tyrosine-kinase inhibitors, with some older patients now managed with TKI plus glucocorticoids and blinatumomab in chemotherapy-free strategies.^[14]
• Older or frail AML — intensive 7+3 is poorly tolerated over about age 75 or with significant comorbidity; azacitidine plus venetoclax (VIALE-A) is the standard lower-intensity option with meaningful remission and survival benefit.^[3]
• Childhood ALL — the commonest childhood cancer; paediatric-inspired regimens cure the great majority of children with standard-risk B-ALL (ETV6-RUNX1, hyperdiploidy — excellent prognosis). Outcomes fall steeply with age, high-risk cytogenetics (hypodiploidy, KMT2A, Ph+), and MRD positivity.^[17]
• Relapsed or refractory ALL — blinatumomab (anti-CD19 BiTE) and inotuzumab (anti-CD22) induce remission, followed by allogeneic SCT or CAR-T (tisagenlecleucel); CD19-negative relapse (antigen escape) is a key pitfall after CD19-directed therapy.^[1][5]
• Therapy-related AML — after alkylating agents or radiotherapy (5 to 7 years latency, monosomy 5 or 7, complex karyotype, adverse) or topoisomerase-II inhibitors (1 to 3 years, KMT2A or RUNX1 rearrangements); poor prognosis; treated with intensive or venetoclax-based therapy, with early transplant consideration.^[1]

Complications and pitfalls

Treatment and disease complications are heavily examined:^[1][2]

• Tumour lysis syndrome — see above; the cardinal pitfalls are failing to prophylax high-burden leukaemia before the first cytotoxic dose, and relying on allopurinol alone (prophylaxis only — it does not clear existing urate) when established TLS needs rasburicase, which degrades uric acid already present.^[7][18]
• APL-associated DIC — catastrophic bleeding (intracranial) and paradoxical thrombosis; the pitfall is delaying ATRA while waiting for cytogenetics, and under-transfusing fibrinogen or platelets.^[2][10]
• Differentiation syndrome (formerly retinoic-acid syndrome) — occurs with ATRA and/or arsenic trioxide in APL: dyspnoea, unexplained fever, weight gain over 5 kg, unexplained hypotension, acute renal failure, and a chest radiograph showing pulmonary infiltrates or pleural or pericardial effusion. Treat immediately with corticosteroids at the first clinical suspicion, and stop ATRA and/or ATO in severe cases or if there is no response. Steroid prophylaxis to prevent the syndrome is of uncertain utility.^[12]
• Leucostasis — see above; the pitfall is not recognising confusion or visual change in a hyperleukocytotic patient as an emergency, or transfusing RBC to a high haematocrit and worsening it.^[6]
• Febrile neutropenia and neutropenic sepsis — the single biggest cause of early treatment-related mortality; the pitfall is delaying antibiotics for culture results.^[1]
• Anthracycline cardiotoxicity — cumulative-dose congestive heart failure (daunorubicin, doxorubicin); pre-treatment echo and lifetime cardiac surveillance.
• Asparaginase toxicity — pancreatitis, hypersensitivity, thrombosis (including sinus-vein thrombosis), hyperglycaemia, low fibrinogen or coagulopathy.
• Intrathecal-chemotherapy errors — wrong drug into the intrathecal space (vincristine is fatal intrathecally); rigid dispensing protocols prevent this. Always dispense vincristine in a mini-bag for IV only and never in a syringe.
• Pancytopenia from treatment — bleeding, infection, anaemia through 2 to 4 weeks of each cycle (nadir).
• Long-term late effects — second cancers, cardiotoxicity, infertility, endocrine failure, osteoporosis, growth impairment in children, neurocognitive effects (especially after cranial irradiation).^[1]

Classic diagnostic pitfalls: delaying ATRA in suspected APL; failing to prevent tumour lysis in a proliferative leukaemia; missing APL on the film (look for abnormal promyelocytes, faggot cells); treating Ph+ ALL without a TKI; relying on a normal or low WBC to exclude leukaemia (15 percent present with leukopenia); confusing a leukaemoid reaction for leukaemia (check LAP, look for cytopenias and clonality); forgetting intrathecal CNS prophylaxis in ALL.^[1]

Prognosis and disposition

Prognosis is determined by age, performance status, cytogenetic or molecular risk (ELN 2022), WBC count, prior myelodysplasia, and response (MRD).^[1]

AML — overall 5-year survival is about 30 percent but stratifies sharply: younger adults with favourable-risk disease (CBF, NPM1 without FLT3-ITD) can achieve 60 to 70 percent long-term survival; adverse-risk (TP53, complex karyotype, monosomy 5 or 7) has 5-year survival below 10 to 20 percent even with transplant; older or unfit patients have median survival under 1 year without venetoclax. Age over 60, poor performance status, WBC over 100, secondary or therapy-related AML and antecedent MDS all worsen prognosis.^[1]

APL — once uniformly fatal within weeks; with ATRA plus arsenic, 2-year event-free survival reached 97 percent in the randomised comparison against ATRA plus chemotherapy, making it the most curable acute leukaemia. Early death before and during induction remains the main challenge.^[2][10]

Core-binding-factor AML (t(8;21), inv(16)) — favourable prognosis, long-term survival 60 to 70 percent with intensive chemotherapy and high-dose cytarabine consolidation; KIT mutations in t(8;21) attenuate this.^[1]

ALL — childhood standard-risk B-ALL has the best outcomes of any leukaemia (the success of paediatric-inspired regimens); adult ALL outcomes fall steeply with age, driven by Ph positivity, high WBC, poor-risk cytogenetics and MRD positivity. Adding a TKI has lifted Ph+ adult ALL into a treatable prognosis.^[13][14]

Measurable residual disease (MRD) — multiparameter flow or molecular (PCR for fusion transcript or NGS) detection of residual leukaemia below morphological threshold — is the strongest predictor of relapse and guides consolidation (MRD positivity pushes toward transplant or trial therapy; MRD-negative deep remission allows de-escalation in some protocols).^[1]

Disposition — all patients are managed by a haemato-oncology multidisciplinary team in a specialist centre, with urgent inpatient admission at diagnosis and during each treatment cycle. The safety-net for the discharging clinician is patient education on febrile neutropenia (a single temperature over 38.3C during neutropenia is an emergency — attend immediately, do not take antipyretics at home), bleeding precautions, and recognition of tumour lysis symptoms.^[1]

Special populations

• Pregnancy — diagnostic workup adapts (avoid CT abdomen or pelvis, prefer MRI, shielded single-view X-ray, defer PET-CT where possible). The priority is treating the maternal disease: untreated acute leukaemia is rapidly fatal to both mother and fetus. Chemotherapy can be given in the 2nd and 3rd trimesters (anthracyclines, cytarabine, vincristine relatively safe; avoid methotrexate in the 1st trimester and throughout where possible; asparaginase carries thrombosis risk). In the 1st trimester, the teratogenicity risk is highest — multidisciplinary timing (defer to 2nd trimester where possible, or deliver then treat). APL in pregnancy — ATRA is relatively safe; arsenic is avoided. Manage with a maternal-fetal-medicine and haematology MDT.^[1]
• Older or frail — the venetoclax plus azacitidine lower-intensity strategy (VIALE-A) has transformed the outlook of unfit AML, with meaningful remission and survival benefit and lower treatment-related mortality than intensive 7+3; best supportive care remains appropriate for the very frail.^[3]
• Down syndrome — neonates may have transient abnormal myelopoiesis (TAM), a self-limiting blast proliferation that resolves spontaneously but carries a 10 to 20 percent later risk of true AML (megakaryoblastic, M7), which is itself unusually chemosensitive in Down-syndrome children (lower-dose protocols).^[1]
• Paediatric — weight-based dosing, CNS prophylaxis (intrathecal, age-adjusted doses), and attention to long-term late effects (growth, endocrine, neurocognitive, second cancers, cardiotoxicity, infertility) drive paediatric-specific protocols. Survivorship care is a lifelong requirement.^[1]
• Immunocompromised (post-transplant, HIV, congenital immunodeficiency) — heightened infection risk (fungal, viral reactivation, PJP) during therapy; aggressive antimicrobial prophylaxis and a lower threshold for empirical treatment.^[1]

Evidence, guidelines and regional differences

Guidelines: ELN 2022 (Dohner et al., Blood) is the international standard for AML diagnosis, genetic risk stratification (favourable, intermediate, adverse) and response criteria; NCCN (US) and BSH (UK) provide parallel operational guidance; WHO 2022 and International Consensus Classification unify the genetic classification of myeloid neoplasms. ICMR and national Indian haematology groups adapt these to local epidemiology and resource constraints.^[1]

Landmark evidence:^[1][2][3][4]

• ELN 2022 (Dohner, Blood 2022) — risk groups, defining genetic abnormalities, response criteria including CRh, and integration of targeted therapy.^[1]
• APL0406 (Lo-Coco, NEJM 2013) — ATRA plus arsenic trioxide was superior to ATRA plus chemotherapy in non-high-risk APL, establishing the chemotherapy-sparing standard.^[2]
• VIALE-A (DiNardo, NEJM 2020) — azacitidine plus venetoclax improved overall survival (14.7 versus 9.6 months) and remission over azacitidine alone in unfit AML.^[3]
• Stone (NEJM 2017) — midostaurin added to standard chemotherapy prolonged overall survival (hazard ratio for death 0.78) and event-free survival in FLT3-mutated AML — the first targeted therapy to do so in this setting.^[4]
• ELIANA (Maude, NEJM 2018) — tisagenlecleucel CAR-T produced durable remissions in relapsed or refractory paediatric B-ALL.^[5]

Regional differences: flow cytometry, allogeneic transplant, venetoclax, midostaurin, blinatumomab and CAR-T are routine in high-income settings but access-limited in India and other low or middle-income countries, where cost and infrastructure drive treatment toward generic 7+3, ATRA-arsenic for APL, palliative regimens, and limited transplant capacity. APL — universal curability with cheap ATRA or arsenic — is a rare equity success story; CAR-T and blinatumomab remain accessible only in specialist centres.^[1]

Controversies: the intensity of therapy in the elderly (intensive 7+3 versus venetoclax-azacitidine — increasingly the latter even for some fit patients); the role of allogeneic transplant in first CR for intermediate-risk AML (driven by MRD); the timing of CAR-T (earlier in relapse versus after salvage); maintenance therapy after transplant; and the cost and equitable access of targeted and cellular therapies.^[1]

The mantra

Twenty percent blasts is the line; Auer rods mean AML and faggot cells mean APL; suspect APL — start ATRA before the genetics return.^[1]

Ward-round test

Stem 1 — the bleeding emergencyShowHide

A 30-year-old presents with petechiae and gum bleeding, film shows abnormal promyelocytes with faggot cells, PT and aPTT prolonged, fibrinogen 0.9, D-dimer high. The cytogenetics will take 48 hours. What do you do now?^[2]

AnswerShowHide

Start ATRA 45 mg per m2 per day immediately on suspicion — do NOT wait for the t(15;17) result. Aggressively correct the coagulopathy: fibrinogen replacement (cryoprecipitate or fibrinogen concentrate), platelets and plasma, rechecking coagulation until stable. Avoid IM injections. Refer to a haematology centre; add arsenic trioxide once PML-RARA is confirmed — early death before and during induction is still what kills APL patients, and delay is the killer.^[11][10][2]

Stem 2 — the high white count and the confusionShowHide

A 65-year-old with AML, WBC 140, becomes confused and dyspnoeic. What is the emergency and the bundle?^[6]

AnswerShowHide

Symptomatic leucostasis — hyperleukocytosis (classically a white-cell count over 100 times 10^9 per L in acute leukaemia). Cytoreduce urgently with leucopheresis and/or hydroxycarbamide, aiming to lower the white-cell count before induction chemotherapy, while managing concurrent tumour lysis and DIC and moving to definitive therapy in parallel.^[6]

Stem 3 — the febrile neutropenicShowHide

A patient on day 10 of induction spikes 38.8C; ANC 0.3. What is the door-to-needle target and the first-line drug?^[9]

AnswerShowHide

Immediate empirical broad-spectrum antibiotics — after blood cultures but before results — covering both gram-positive and gram-negative pathogens: an anti-pseudomonal beta-lactam such as piperacillin-tazobactam (a carbapenem if septic shock or resistant organism). Add vancomycin for suspected gram-positive line infection or haemodynamic instability. Every patient with fever and neutropenia must be treated swiftly and broadly.^[9]

Stem 4 — the adult ALL and the chromosome that changes everythingShowHide

A 45-year-old with ALL is found to have t(9;22) BCR-ABL1. What is added to chemotherapy, and why does it matter?^[13][14]

AnswerShowHide

Add a tyrosine-kinase inhibitor — TKIs transformed Ph+ ALL from the worst-prognosis adult ALL into a treatable disease. The newest frontline approach is chemotherapy-free: dasatinib plus glucocorticoids followed by blinatumomab, with complete remission in 98 percent and 95 percent overall survival at 18 months' follow-up.^[14]

^[7]

References18ShowHide

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2. [2]Lo-Coco F, Avvisati G, Vignetti M, et al. Retinoic acid and arsenic trioxide for acute promyelocytic leukemia N Engl J Med, 2013.PMID 23841729
3. [3]DiNardo CD, Jonas BA, Pullarkat V, et al. Azacitidine and Venetoclax in Previously Untreated Acute Myeloid Leukemia N Engl J Med, 2020.PMID 32786187
4. [4]Stone RM, Mandrekar SJ, Sanford BL, et al. Midostaurin plus Chemotherapy for Acute Myeloid Leukemia with a FLT3 Mutation N Engl J Med, 2017.PMID 28644114
5. [5]Maude SL, Laetsch TW, Buechner J, et al. Tisagenlecleucel in Children and Young Adults with B-Cell Lymphoblastic Leukemia N Engl J Med, 2018.PMID 29385370
6. [6]Ganzel C, Becker J, Mintz PD, et al. Hyperleukocytosis, leukostasis and leukapheresis: practice management Blood Rev, 2012.PMID 22364832
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8. [8]Cairo MS, Coiffier B, Reiter A, Younes A Recommendations for the evaluation of risk and prophylaxis of tumour lysis syndrome (TLS) in adults and children with malignant diseases: an expert TLS panel consensus Br J Haematol, 2010.PMID 20331465
9. [9]Freifeld AG, Bow EJ, Sepkowitz KA, et al. Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the infectious diseases society of america Clin Infect Dis, 2011.PMID 21258094
10. [10]Sanz MA, Fenaux P, Tallman MS, et al. Management of acute promyelocytic leukemia: updated recommendations from an expert panel of the European LeukemiaNet Blood, 2019.PMID 30803991
11. [11]Warrell RP Jr, Frankel SR, Miller WH Jr, et al. Differentiation therapy of acute promyelocytic leukemia with tretinoin (all-trans-retinoic acid) N Engl J Med, 1991.PMID 1850498
12. [12]Stahl M, Tallman MS Differentiation syndrome in acute promyelocytic leukaemia Br J Haematol, 2019.PMID 31410848
13. [13]Terwilliger T, Abdul-Hay M Acute lymphoblastic leukemia: a comprehensive review and 2017 update Blood Cancer J, 2017.PMID 28665419
14. [14]Foà R, Bassan R, Vitale A, et al. Dasatinib-Blinatumomab for Ph-Positive Acute Lymphoblastic Leukemia in Adults N Engl J Med, 2020.PMID 33085860
15. [15]Khoury JD, Solary E, Abla O, et al. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms Leukemia, 2022.PMID 35732831
16. [16]Taylor FB Jr, Toh CH, Hoots WK, et al. Towards definition, clinical and laboratory criteria, and a scoring system for disseminated intravascular coagulation Thromb Haemost, 2001.PMID 11816725
17. [17]Hunger SP, Mullighan CG Acute Lymphoblastic Leukemia in Children N Engl J Med, 2015.PMID 26465987
18. [18]Lopez-Olivo MA, Pratt G, Palla SL, Salahudeen A Rasburicase in tumor lysis syndrome of the adult: a systematic review and meta-analysis Am J Kidney Dis, 2013.PMID 23684124