Acute leukemia

Acute leukemia is a malignant neoplastic disease that arises from either the lymphoid cell line (acute lymphoblastic/lymphocytic/lymphoid leukemia, ALL) or the myeloid cell line (acute myeloid/myelogenous/myelocytic leukemia, AML). ALL is the most common childhood malignancy, whereas AML primarily affects adults. An underlying cause is rarely identifiable, but risk factors include prior chemotherapy and radiation therapy, as well as hereditary syndromes such as Down syndrome. AML is also associated with pre-existing hematologic disorders (e.g., myelodysplastic disorder, myeloproliferative disorders). Acute leukemias are characterized by the proliferation in the bone marrow of immature, nonfunctional white blood cells (“blasts”) that impair normal hematopoiesis and lead to pancytopenia manifesting with symptoms and signs of anemia (↓ RBCs), clotting disorders (↓ thrombocytes), and increased susceptibility to infection (↓ fully functional, mature WBCs). Leukemic cells also infiltrate extramedullary organs, resulting in hepatosplenomegaly and, less commonly, involvement of the skin, CNS, and/or scrotum. Patients with AML, in particular, may develop extremely high WBC counts, increasing the risk of leukostasis and DIC. The first diagnostic steps include a complete blood count and peripheral blood smear to determine the WBC count and the presence of blasts. Bone marrow biopsy or aspiration with subsequent cytogenetic analysis and immunophenotyping confirm the diagnosis. A chemotherapy regimen consisting of high-dose (induction) and low-dose (consolidation and maintenance) cycles is the mainstay of treatment. Additional measures, such as allogeneic stem cell transplantation, may be indicated in patients with poor prognostic factors (e.g., unfavorable cytogenetics) or if initial chemotherapy fails.

• Acute lymphoblastic leukemia ^[1]
  • Peak incidence: 2–5 years
  • Most common malignant disease in children
  • ∼ 80% of acute leukemias during childhood are lymphoblastic.
  • ♂ > ♀
• Acute myeloid leukemia ^[2]
  • Peak incidence: 65 years
  • 80% of acute leukemias during adulthood are myelogenous.

Epidemiological data refers to the US, unless otherwise specified.

Acute lymphoblastic leukemia (ALL)

• No identifiable cause or risk factors in most cases
• Prior bone marrow damage due to alkylating chemotherapy or ionizing radiation
• Adult T-cell leukemia/lymphoma is linked to infection with HTLV. ^[3][4][5]
• Genetic or chromosomal factors
  • Down syndrome: Risk of ALL is, like that of AML, 10–20 times higher in patients with Down syndrome compared to the general population. ^[6][7]
  • Neurofibromatosis type 1
  • Ataxia telangiectasia ^[1]

Acute myeloid leukemia (AML)

• No identifiable cause or risk factors in most cases
• Pre-existing hematopoietic disorder (most common identifiable cause) ^[8]
  • Myelodysplastic syndromes
  • Aplastic anemia
  • Myeloproliferative disorders (e.g., osteomyelofibrosis; , CML)
• Environmental factors ^[2]
  • Alkylating chemotherapy
  • Ionizing radiation
  • Benzene exposure
  • Tobacco
• Genetic or chromosomal factors
  • Down syndrome: The risk of AML is, like that of ALL, 10–20 times higher in patients with Down syndrome compared to the general population. ^[7]
  • Fanconi anemia

References:^[9][10]

ALL ^[1]

• French-American-British (FAB) historical classification of ALL
  • L1 ALL with small cells (20–30%)
  • L2 ALL with heterogeneous large cells (70%)
  • L3 ALL with large cells, i.e., Burkitt lymphoma (1–2%)
• The current WHO Classification (2016) classifies ALL into subtypes of precursor lymphoblastic leukemia/lymphoma based on morphologic and genetic factors:
  • B lymphoblastic leukemia with recurrent genetic abnormalities
    • ALL with BCR-ABL
    • ALL with t(v;11q23)
    • ALL with t(1;19)(q23;p13.3)
    • ALL with t(12;21)(p13;q22)
    • Hyperdiploid > 50
    • Hypodiploid
    • t(5;14)(q31;q32)
  • B lymphoblastic leukemia, not otherwise specified
  • Precursor T lymphoblastic leukemia/lymphoma
• Immunophenotype classification of ALL: based on the origin (B cell or T cell) and maturity of the leukemic cells
  • B-cell ALL (∼ 80–85% of cases) ^[11]
    • Early (pro-B) ALL
    • Common ALL
    • Precursor B-ALL
    • Mature B-cell ALL (also known as Burkitt leukemia)
  • T-cell ALL (∼ 15–20% of cases)
    • Early (pro-T) ALL
    • Intermediate-T ALL
    • Mature T-cell ALL

AML

• The French-American-British (FAB) classification distinguishes between eight subtypes of AML, according to the histopathological appearance of the cells.

FAB classification for AML
M0	Acute myeloblastic leukemia without maturation
M1	Acute myeloblastic leukemia with minimal granulocyte maturation
M2	Acute myeloblastic leukemia with granulocyte maturation
M3	Acute promyelocytic leukemia (APL)
M4	Acute myelomonocytic leukemia
M5	Acute monocytic leukemia
M6	Acute erythroid leukemia
M7	Acute megakaryoblastic leukemia

• The WHO classification is based on various factors (e.g., presence of genetic abnormalities or associations to prior chemotherapy/radiation).
  • AML with recurrent genetic abnormalities (e.g., translocations)
  • AML with myelodysplasia-related changes
  • Therapy-related AML
  • AML not otherwise specified
  • Myeloid sarcoma
  • Myeloid leukemia associated with Down syndrome

References:^[8][12]

• Acquired somatic mutations (chromosomal translocations and other genetic abnormalities) in early hematopoietic precursors; → clonal proliferation of a lymphoid or myeloid stem cell line and arrest in cell differentiation and maturation in early stages of hematopoiesis; → rapid proliferation of abnormal and dysfunctional blasts (with impaired apoptosis pathways) → accumulation of leukemic white blood cells in the bone marrow → disrupted normal hematopoiesis → leukopenia (↑ risk of infections); , thrombocytopenia (↑ bleeding); , and anemia
• Immature blasts enter the bloodstream → infiltration of other organs (particularly the CNS, testes, liver, and skin)

References:^[13][8][14]

Clinical features are either related to bone marrow failure, infiltration of organs by leukemic cells, or a combination of both.

General features of acute leukemia
Sudden onset of symptoms and rapid progression (days to weeks) Anemia: fatigue, pallor, weakness Thrombocytopenia: epistaxis, bleeding gums, petechiae, purpura Immature leukocytes: frequent infections, fever Hepatosplenomegaly (caused by leukemic infiltration) [2] Signs of oncologic emergencies: can be the first sign of leukemia, e.g., an elderly patient presenting with priapism or DIC may be a sign of leukostasis (more common in AML than ALL) See “Complications” below for details.
Clinical features of ALL	Clinical features of AML
Fever, night sweats, unexplained weight loss Painless lymphadenopathy Bone pain (presenting as limping or refusal to bear weight in children) Airway obstruction (stridor, difficulty breathing) due to mediastinal or thymic infiltration (primarily in T-cell ALL) [15][16] Features of SVC syndrome Meningeal leukemia (or leukemic meningitis) → headache, neck stiffness, visual field changes, or other CNS symptoms (caused by CNS involvement) [1][16] Testicular enlargement (rare finding)	Leukemia cutis (or myeloid sarcoma): nodular skin lesions with a purple or gray-blue color Gingival hyperplasia (AML subtype M4 and M5) Signs of CNS involvement, e.g., headache, visual field changes (uncommon)

Fever and lymphadenopathy are rare in AML, but can be common first signs in ALL!

Fever in a patient with acute leukemia must always be treated as a sign of infection until proven otherwise!

Remember metastasis for ALL by thinking of the following: ALL metaStaSizeS to the CNS and teSteS.

References:^{[17][1][15][16]}

Approach

• Initial tests: CBC; and peripheral blood smear; (determine WBC count and the presence of blasts)
• Confirmatory test: bone marrow aspiration and biopsy (examine morphology, histochemistry, cytogenetics, and immunophenotyping)
• Further tests: if organ involvement is suspected (e.g., imaging, CSF analysis)

Laboratory studies

• Complete blood count
  • Leukocytes: The white blood cell count (WBC) may be elevated, normal, or low and is not a reliable diagnostic marker.
    • Leukemic hiatus in AML: A gap in the differentiation of white blood cells in which there is a high number of blast cells and mature leukocytes but no intermediate forms
  • Thrombocytopenia
  • Anemia
• Peripheral blood smear: presence of blasts
  • AML
    • ↑ Myeloblasts
    • Some subtypes (especially M3, or APL) exhibit Auer rods
      • Pink-red, rod-shaped granular cytoplasmic inclusion bodies in malignant immature myeloblasts or promyelocytes
      • Auer rods are myeloperoxidase positive.
  • ALL: ↑ lymphoblasts
• Additional laboratory studies
  • Coagulation studies: rule out DIC
  • Electrolytes and metabolic markers: ↑ PO₄^3-, ↓ Ca²⁺, ↑ K⁺, ↑ LDH, and ↑ uric acid indicate increased cell lysis

Bone marrow aspiration and biopsy

• Confirmatory diagnostic tests
  • AML: > 20% myeloblasts in the bone marrow ^[18]
  • ALL: > 20% lymphoblasts in the bone marrow ^[19]

Morphology, histochemistry, cytogenetics, and immunophenotyping in ALL and AML
		ALL	AML
Morphology [20][21]		Large blasts (1.5–3 times the size of RBC) Blasts with large, irregular nuclei (high nuclear-to-cytoplasm ratio) Inconspicuous nucleoli Coarse granules No Auer rods	Large blasts (2–4 times the size of RBC) Blasts with round or kidney-shaped nuclei, comparatively more cytoplasm than in ALL Prominent nucleoli Fine granules Auer rods (present in 50% of cases) [22]
Histochemistry	Myeloperoxidase (found in peroxidase-positive granules)	Negative	Positive
	Terminal deoxynucleotidyl transferase (TdT)	Positive	Negative
	Periodic acid-Schiff (PAS)	Often positive	Negative
Cytogenetics [16][9]		Philadelphia translocation (∼ 20–30% of ALL in adults and only 2–3% of ALL in children) t(12;21): most common specific abnormality in childhood B-ALL Hyperdiploidy is common in pre-B-ALL (see prognosis below)	t(15;17) translocation (particularly acute promyelocytic leukemia (M3 AML) [23][24] Philadelphia translocation (< 2% of patients with AML)
Immunophenotyping by flow cytometry		B-ALL is usually positive for CD10 (CALLA): marker for immature B lymphocytes (pre-B) CD19 CD20 T-ALL is usually positive for CD2–CD8, especially CD3	The majority of subtypes are positive for CD13, 33, 34, 117, and HLA-DR.

Myelogenous leukemia is myeloperoxidase positive.

Further tests

• Cerebrospinal fluid analysis: relevant for diagnosis and treatment of leukemic meningitis
• Chest x-ray: mediastinal mass in the case of thymic infiltration (occurs primarily in T-cell ALL) or mediastinal lymphadenopathy
• Abdominal ultrasound: organ enlargement (especially the liver and/or spleen)

References:^{[23][25][2][1][15][24][9][26][16][12]}

Approach

• Aggressive chemotherapy is the mainstay of treatment; prognosis is good with treatment.
• Radiation and/or targeted therapy are considered depending on the type and stage of disease.
• Allogeneic stem cell transplantation is indicated in patients with poor prognostic factors or who do not achieve remission with chemotherapy.
• Supportive measures are vital to manage severely immunocompromised patients and prevent treatment-related complications.

Chemotherapy

Chemotherapy regimens are comprised of induction, followed by consolidation, and finally maintenance therapy. The choice of chemotherapeutic agents is based on the cytogenetics of the leukemic cells. ^[21]

1. Induction therapy (goal: massive reduction of tumor cell count)
   • Duration: 4–6 weeks
   • High-dose chemotherapy regimens are effective but usually cause severe side effects.
2. Re-induction therapy (goal: massive reduction of tumor cell count)
   • Only indicated in case of relapse or failure of primary induction therapy
   • Duration: 4–6 weeks
3. Consolidation therapy (goal: destruction of remaining tumor cells)
   • Begin after complete remission is achieved
   • Duration: several months
   • Medium doses
   • ALL regimen: variable drug regimens
4. Maintenance therapy (goal: maintaining remission)
   • Duration: up to 24 months
   • Low doses
   • ALL regimen: may include methotrexate, vincristine; , glucocorticoids

Common agents used in the initial treatment of acute leukemia
	ALL [27][28]	AML
Standard regimen	Vincristine Glucocorticoids Cyclophosphamide Doxorubicin L-asparaginase	Cytarabine Anthracyclines (e.g., daunorubicin) For APL (promyelocytic leukemia): Both of these drugs induce the maturation of immature malignant cells. ATRA (all-trans retinoic acid) Arsenic
Philadelphia translocation	Addition of BCR-ABL tyrosine kinase inhibitor (e.g., imatinib)

85% of children with ALL achieve complete remission with chemotherapy! ^[21]

A t(15;17) translocation causes the retinoic acid receptor to change, preventing myeloblast differentiation from occurring under physiologic levels of retinoic acid. Thus, high doses of all-trans-retinoic acid (vitamin A) may induce remission by causing malignant cells to mature.

Preventive CNS treatment ^{[29][14][30][31][32][33]}

• Intrathecal chemotherapy: chemotherapeutic therapy administered directly into the subarachnoid space via spinal tap or a device placed under the scalp
  • ALL: indicated for all children to prevent meningeal leukemia (even if no CNS involvement is detected)
  • AML: only indicated after diagnostic measures have confirmed CNS involvement
• CNS radiotherapy
  • Not routinely used because of associated risk of secondary malignancies and endocrine (e.g., hypothyroidism, growth hormone deficiency) and neurocognitive (e.g., cognitive decline, neuroinflammation) side effects.
  • Reserved for patients who do not respond to intrathecal chemotherapy or who develop impingement of important CNS structures (e.g., cranial nerve, spinal cord).

Allogeneic stem cell transplantation

• Indication: poor prognostic factors (e.g., unfavorable cytogenetics); or patients who do not achieve remission through chemotherapy

Supportive therapy ^[12][21]

• Preventing infection is very important as patients are severely immunocompromised.
  • Surveillance: regular inspection of oropharynx, skin, and catheter sites; regular chest x-rays or CT to detect pulmonary infection
  • Advise patients to pay special attention to personal hygiene (e.g., daily bathing and tooth brushing, cleaning of minor wounds, maintaining a germ-free environment; i.e., avoiding crowds and contact with sick individuals, wearing a face mask outside if WBC counts are low)
  • Antibiotic prophylaxis in afebrile neutropenic patients is controversial
    • If infection is suspected or neutropenia and fever are present: IV broad-spectrum antibiotics (see neutropenic fever)
  • PCP prophylaxis with TMP-SMX in all neutropenic patients
  • Mucositis prophylaxis with local antimycotics
  • Herpes simplex prophylaxis with acyclovir
  • Updating immunizations
  • Colony-stimulating factor administration can be considered for febrile neutropenia
• Managing treatment side effects
  • Antiemetics (e.g., ondansetron)
  • Enteral and parenteral nutritional support
  • Transfusion for severe cytopenia
• Uric acid stone prophylaxis: begin prior to chemotherapy to prevent hyperuricemia and urate induced nephropathy
  • Hydration and fluid administration
  • Allopurinol and rasburicase (see tumor lysis syndrome below)

References:^{[23][34][35][29][36][27][24][37]}

Oncologic emergencies

• Mediastinal or thymic infiltration (primarily in T-cell ALL) → SVC syndrome, airway compromise
• Febrile neutropenia
• Severe thrombocytopenia; or anemia

Leukostasis

• Description: : ↑ blood viscosity caused by an excessive number of leukocytes (usually > 150,000/mm³ in patients with AML and > 400,000/mm³ in patients with ALL)
• Pathophysiology: : very high number of immature leukocytes → increased viscosity of blood → increased risk of vascular obstruction → cerebral and pulmonary complications, DIC
• Occurrence: more common in AML than ALL
• Clinical features
  • Chest pain (ischemic injury)
  • Headache, altered mental status, cranial nerve disorders
  • Priapism
  • DIC: frequent complication of APL
• Treatment
  • Cytoreduction: hydroxyurea with or without leukapheresis to rapidly reduce WBC count
  • Preventive measures for tumor lysis syndrome (see “Prophylaxis” below)

Tumor lysis syndrome (TLS) ^[38]

• Description: The rapid destruction of tumor cells leads to a massive release of intracellular components, which subsequently damage the kidneys and may cause potentially life-threatening renal failure.
• Etiology: mostly occurs after initiating cytotoxic treatment of ALL, AML, or NHL
• Pathophysiology: tumor cell lysis → release of intracellular components (e.g., K⁺, PO₄^3-, nucleic acid) into the bloodstream
  • Hyperkalemia
  • Hyperphosphatemia: PO₄^3- binds Ca²⁺ and forms calcium phosphate crystals that obstruct renal tubules → acute kidney injury
  • ↓ Ca²⁺ secondary to PO₄^3- binding → hypocalcemia
  • ↑ Nucleic acid → conversion to uric acid → hyperuricemia → urate nephropathy and risk of acute renal injury
• Clinical features
  • Nausea, vomiting, and diarrhea
  • Lethargy
  • Hematuria
  • Seizures
  • Cardiac arrhythmias
  • Tetany, muscle cramps
  • Paresthesia
• Prophylaxis
  • All patients
    • Hydration (most effective preventive measure)
    • Avoid potentially nephrotoxic drugs such as NSAIDs
  • Possibly in addition to hydration
    • In patients with a low to intermediate risk of TLS: allopurinol
    • In patients with a high risk of hyperuricemia due to TLS (e.g., extremely high WBC): rasburicase, a recombinant uricase, which catalyzes the breakdown of uric acid to allantoin
    • Consider alkalinization of the urine
• Treatment
  • Treat electrolyte abnormalities
    • Hyperkalemia
      • Glucose and insulin (rapid action)
      • Sodium polystyrene sulfonate (delayed action)
      • Last resort: hemodialysis or hemofiltration
    • Hypocalcemia: calcium administration
    • Hyperphosphatemia: hydration and possibly phosphate binding agents
  • Rasburicase, if not already given as prophylaxis
  • Fluid administration with or without loop diuretics to aid renal excretion of uric acid crystals
  • Renal replacement therapy may be necessary

“PUKE calcium” for the electrolytes affected in tumor lysis syndrome: Phosphorus, Uric acid, and potassium (K⁺) are Elevated; Calcium is decreased.

References:^[39][40]

We list the most important complications. The selection is not exhaustive.

5-year survival rate following treatment

• ALL: The 5-year survival rate is generally higher compared to AML (varies from ∼ 20% in elderly patients to ∼ 80% in children and adolescents)
• AML: ∼ 30%, but it varies according to the patient's age. The survival time has increased more recently due to improvements in treatment.

Unfavorable prognostic factors

	ALL	AML
Age	< 1 year or > 10 years	> 60 years
Disease features	WBC count > 50,000/mm3 CNS involvement at diagnosis	↑ LDH FAB M7 (acute megakaryocytic leukemia)
Cytogenetics
	Philadelphia chromosome t(9;22) Hypoploidy Complex pattern of aberrations (> 3 aberrations)	Various translocations, e.g., t(6;9) Karyotype abnormalities (e.g., trisomy 8, monosomy 5 or 7) FLT3 gene mutation Complex pattern of aberrations (i.e., > 3 aberrations)
Immunotyping	Mature B-cell ALL Precursor T-cell ALL	CD34 MDR1

Favorable prognostic factors

ALL	AML
< 50,000/mm3 No CNS involvement t(12;21) Hyperploidy	t(8;21) Acute promyelocytic leukemia (APL) with t(15;17)

To remember that translocation t(12;21) commonly manifests with pediatric B-ALL and usually has a favorable outcome, think: “Kids flip back to health!” (the number 12 is 21 flipped around).

References:^{[41][42][43][21][44][45]}