- Clinical science
Acute leukemia
Summary
Acute leukemia is a malignant neoplastic disease that arises from either the lymphoid cell line (acute lymphoblastic/lymphocytic/lymphoid leukemia, or ALL) or the myeloid cell line (acute myeloid/myelogenous/myelocytic leukemia, or 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.
Epidemiology
-
Acute lymphoblastic leukemia [1]
- Peak incidence: 2–5 years
- Most common malignant disease in children
- ∼ 80% of acute leukemias during childhood are lymphocytic.
- ♂ > ♀
- Acute myeloid leukemia [2]
Epidemiological data refers to the US, unless otherwise specified.
Etiology
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
Acute myeloid leukemia (AML)
- No identifiable cause or risk factors in most cases
- Pre-existing hematopoietic disorder (most common identifiable cause) [8]
-
Environmental factors [2]
- Alkylating chemotherapy
- Ionizing radiation
- Benzene exposure
- Tobacco
- Genetic or chromosomal factors
References:[9][10]
Classification
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:
-
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
-
B-cell ALL (∼ 80–85% of cases) [11]
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).
References:[8][12]
Pathophysiology
- 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 liver, spleen, lymph nodes, but also testes, skin, and mediastinum)
References:[13][8][14]
Clinical features
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 | |
---|---|
| |
Clinical features of ALL | Clinical features of AML |
|
|
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!
References:[17][1][15][16]
Diagnostics
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
-
Leukocytes: The white blood cell count (WBC) may be elevated, normal, or low and is not a reliable diagnostic marker.
-
Peripheral blood smear: presence of blasts
- AML: Some subtypes (especially M3, or APL) exhibit Auer rods; , which are pink-red, rod-shaped granular cytoplasmic inclusion bodies in malignant immature lymphocytes (blasts)
-
Additional laboratory studies
- Coagulation studies: rule out DIC
- Electrolytes and metabolic markers: ↑ PO42-, ↓ 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] | |||
Histochemistry | Myeloperoxidase (found in peroxidase-positive granules) |
|
|
Terminal deoxynucleotidyl transferase (TdT) |
|
| |
Periodic acid-Schiff (PAS) |
|
| |
Cytogenetics [16][9] |
|
| |
Immunophenotyping by flow cytometry |
|
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]
Treatment
Approach
- Aggressive chemotherapy is the mainstay of 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]
-
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.
-
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
-
Consolidation therapy (goal: destruction of remaining tumor cells)
- Begin after complete remission is achieved
- Duration: several months
- Medium doses
- ALL regimen: variable drug regimens
-
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 acute leukemia | ||
---|---|---|
ALL [27][28] | AML | |
Standard regimen |
| |
Philadelphia translocation |
|
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 occuring 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
-
Intrathecal chemotherapy: chemotherapetic 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).
References:[29][14][30][31][32][33]
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]
Complications
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 vessel 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
-
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+, PO43-, nucleic acid) into the bloodstream
- Hyperkalemia
- Hyperphosphatemia: PO43- binds Ca2+ and forms calcium phosphate crystals that obstruct renal tubules → acute kidney injury
- ↓ Ca2+ secondary to PO43- 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 TLS (e.g., extremely high WBC): rasburicase (urate oxidase)
- Consider alkalinization of the urine
- All patients
-
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
-
Hyperkalemia
- 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
- Treat electrolyte abnormalities
“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.
Prognosis
5-year survival rate following treatment
- ALL: generally better than with 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 |
|
|
Disease features |
|
|
Cytogenetics | ||
| ||
Immunotyping |
|
|
Favorable prognostic factors
ALL | AML |
---|---|
|
|
The most common specific abnormality in childhood B-ALL is the t(12;21) translocation, which is associated with a favorable outcome.
References:[41][42][43][21][44][45]