Acute myeloid leukemia (AML) is a common clinical leukemia, and with the rapid development of medical science, its diagnosis and treatment have made great progress. Recently, the World Health Organization (WHO) organized more than 100 internationally renowned hematopathologists, clinical and related experts to develop a new classification of hematopoietic myeloid disorders based on new findings in evidence-based medicine, clinical and pathological research. This classification integrates cellular morphology, immunological markers, cytogenetics and clinical features, and classifies AML into four types and 19 types, which are named in the table below.
WHO classification of AML
AML with specific cytogenetic abnormalities
AML with t(8;21)(q22;q22), (AML1/ETO)
Acute promyelocytic leukemia with t(15;17)(q22;q11~22),(PML/RARa) and variants
AML with bone marrow abnormal eosinophils and inv(16)(p13;q22) or t(16;16)(p13;q22),(CBFβ/MYH11)
AML with 11q23 (MLL)
AML with multilineage pathological hematopoiesis
History of MDS or MDS/MPD
No history of MDS or MDS/MPD, but two or more lineages of pathological hematopoiesis (R50% pathological cells)
Treatment-related AML and MDS
Alkylating agent-related
Topoisomerase II inhibitor-related
Other types
Other types of AML (those who do not fit the above types)
AML, minimally differentiated
AML, immature
AML with maturation
Acute monocytic leukemia (AMML)
Acute monocytic leukemia
Acute red leukemia (erythroleukemia/leukemia and pure red leukemia)
Acute megakaryocytic leukemia
Acute basophilic leukemia
Acute panmyelosis with myelofibrosis
Myeloid leukemia sarcoma
1. Prerequisites for the diagnosis of WHO classification of myeloid malignant hematologic diseases
The key to the diagnosis of AML is to determine the cell lineage of origin and the degree of differentiation of the malignant clonal cells. Similar to FAB and PVSG (True Erythrocytosis Study Group), WHO classification also determines the cell lineage and degree of differentiation of leukemic cells based on their morphology, cytochemistry and their immunophenotypic characteristics.
1.1 Determination of “primitive cells” in leukemia “primitive cells” are of practical importance not only for correct typing and diagnosis, but also for prognosis. Counting primary cells requires sorting 200 and 500 cells in May-Grunwald Giemsa stained blood and bone marrow slices, respectively, and verifying with a bone marrow biopsy if necessary. In acute monocytic and megakaryocytic leukemia, the proportion of primitive cells refers to the number of primitive (juvenile) mono- and promyelocytes, while in APL abnormal promyelocytes are counted, the latter may have reniform or bilobed nuclei, the cytoplasm contains coarse granules and often bundles of Auer vesicles, sometimes the cytoplasm lacks granules. Except for pure erythroid leukemia, primitive erythrocytes are usually not included in the “primitive cell” ratio.
Cytochemical stains such as myeloperoxidase (POX), nonspecific esterase (NSE) and its sodium fluoride inhibition test are still the routine methods. Determination of cellular immunophenotype is important to determine their origin, usually by flow cytometry. Positive CD34, CD117, CD13, D33, CD15, CD41 and CD61 should be the golden indicators of myeloid cells.
1.3 Cytogenetic examination is an important component of WHO classification of subtypes The main methods are chromosomal examination, reverse transcription polymorphism chain reaction (RT-PCR) and fluorescence in situ hybridization (FISH). In view of the importance of genetic diagnosis in WHO typing, it is recommended that chromosomal examination be routinely performed in patients with initial diagnosis, and that the expression of abnormal genes by chromosome, RT-PCR or FISH be reviewed regularly in patients with specific chromosomal abnormalities to guide treatment.
2. Principles of diagnostic classification of AML leukemia
To summarize the clinical practice of the FAB Collaborative Group on AML classification: ① Some AML often have specific abnormal chromosomal nuclear gene expression, and there is a certain relationship with its morphological characteristics, response to chemotherapy and prognosis. For example, AML-M2 is often associated with t(8;21)(q22;q22) (AML/ETO), AML-M3 with t(15;17)(q22;q12) (PML/RARα), AML-M4Eo with inv(16)(p13q22) or t(16;16)(p13;q22) (CBFβ/MYH11), etc. In these types, specific morphological alterations often predict specific genetic abnormalities that better reflect the clinical prognosis of the biological features of leukemic cells. However, morphological features and genetic abnormalities do not directly correlate in a significant number of leukemic patients; in other words, the molecular and genetic defects in these patients are heterogeneous, so it is necessary to distinguish between AML with and without specific chromosomal and genetic abnormalities; (2) numerous clinical observations have confirmed that AML accompanied by myeloid multilineage proliferation abnormalities or transformation from myelodysplastic syndrome (MDS) to The pathogenesis and cell biology of AML is completely different from those without myelodysplasia. The former often have non-random cytogenetic abnormalities, especially loss of genetic material, and have a poor clinical prognosis in response to chemotherapy. Therefore, the former is considered as a separate subtype of AML in WHO classification; (3) AML without myelodysplasia and above specific chromosomal abnormalities mostly responds well to chemotherapy and is also seen in children and young patients, with a better overall prognosis, and is treated as other types in WHO classification. Some specific types are also included, with some differences in their cell biology and prognosis. Thus, the WHO classification differs from the FAB classification in that the former combines cytomorphological, immunological markers, cytogenetic and clinical features, and each biological subtype becomes a separate disease. The percentage of myeloid leukemia primitive cells for the diagnosis of AML was also redefined, i.e., the percentage of primitive cells in bone marrow and blood for the diagnosis of AML was reduced from 30% to 20%. However, for patients with specific clonal chromosomal or genetic markers, such as t(8;21)(q22;q22), t(15;17)(q22;q12) ,inv(16)(p13q22) or t(16;16)(p13;q22), the diagnosis of AML can be established even if the percentage of primitive cells in bone marrow and blood does not reach 20%.
Many studies have confirmed that patients with a proportion of leukemic progenitor cells in the bone marrow of 20%-<30% have the same clinical features (including response to chemotherapy and survival) > as those with 30%, and are classified as MDS-RAEBt according to the FAB classification, while such patients are classified as AML with multilineage pathological hematopoiesis in the WHO classification, regardless of the patient’s history of MDS. Numerous studies have confirmed that MDS-RAEBt and MDS-associated AML share the same cell biology and clinical features, such as similar cell proliferation kinetics and apoptotic properties, but are different from other types of MDS. In both cases, chromosomal and genetic alterations such as chromosome 7 and complex chromosomal abnormalities, high expression of multidrug resistance proteins, and poor response to chemotherapy are associated with poor prognosis. Furthermore, according to the International Risk Factor Assessment Group for MDS (IRAW), RAEBt is not an inert disease, and its rates of leukoreversion at 2-3, 3 months and 1 year are 25%, 50% and more than 60%, respectively, with its median survival time not exceeding 1 year. In view of this, the current WHO classification considers MDS-RAEBt to be the same disease as AML with multilineage pathological hematopoiesis, and relies on not only the percentage of primary cells but also clinical, cytological and genetic features and disease progression in the treatment strategy.
Taken together, the WHO classifies AML into 4 subtypes, namely:
① AML with specific cytogenetic abnormalities;
(ii) AML with multilineage pathological hematopoiesis;
(iii) treatment-related AML and MDS;
Finally, those who did not fit the above categories were classified as ④ other types of AML.
3. Characteristics of AML subtypes
3.1 AML with specific cytogenetic abnormalities
This subtype contains 5 types in the WHO classification (see table). The first 4 types are currently better understood, they account for about 30% of AML and are generally first-onset patients. Among them, the genetic abnormalities of t(15;17)(q22;q12) (PML/RARα) and inv(16)(p13q22) or t(16;16)(p13;q22) (CBFβ/MYH11) are closely related to their morphological features, and most patients can anticipate their cytogenetic abnormalities from microscopic observation of bone marrow cell morphology. In particular, they are considered to be truly clinico-pathologically and genetically distinct and independent diseases because they are clinically distinct and respond well to chemotherapy in particular. Although the cellular morphology of those with 11q23 abnormalities is often granulocytic or mature monocytic, those with such cellular morphological features are unlikely to have any degree of foreknowledge of their genetic abnormalities. It is important to note that although this subtype is often primary, they are involved in genes that are susceptible to damage by some chemotherapy, particularly topoisomerase II inhibitors, which are therapeutically relevant in AML, and a careful history is important for the differential diagnosis.
With further studies, the subtypes (disease types) included in this group may be further increased, such as t(8;16), t(6;9), and t(3;3), etc. Their alterations are also often associated with certain morphological and clinical features, however, the relationship with prognosis and other subtypes cannot be fully distinguished yet. t(3;3) abnormalities are often associated with MDS-related AML, so they can be categorized as The t(3;3) abnormality is often associated with MDS-related AML, so it can be classified as one of the AML types with multilineage pathological hematopoiesis. On the other hand, in clinical practice, genetic data are often not available or absent in a timely manner, and some morphological features are not fully consistent with abnormal genes, such as t(16;16)(p13;q22) (CBFβ/MYH11) which is only detected in 30%-100% of M4Eo, so cytogenetic and genetic results should be obtained as much as possible in clinical practice.
3.2 AML with multilineage pathological hematopoiesis
It is well established that MDS-associated AML is unique and important in terms of clinical and cytobiological features, and therefore AML with multilineage pathological hematopoiesis is considered as a subtype. The diagnosis of AML is easier if the patient had MDS/MPD before the diagnosis of AML (at least 6 months), and more difficult if not. For practical and widespread convenience, the diagnosis of the latter is mainly based on morphology, i.e., regardless of the history of MDS before AML, AML with multilineage pathological hematopoiesis can be diagnosed in patients with ≥ 20% of primitive cells in bone marrow and blood and ≥ 50% of myeloid cells of two or more lineages with pathological hematopoiesis. The latter does not affect the prognosis of patients with better prognosis and pathological hematopoiesis, and similarly
The prognosis of patients with poorer prognosis genetic alterations and pathological hematopoiesis may not be worse. Therefore, in future clinical practice, it is necessary to explore the possibility of a combined cytogenetic and morphological classification for these patients.
3.3 Treatment-related AML and MDS
These patients can be divided into two categories according to their previous treatment: alkylator/radiation therapy-related and topoisomerase II inhibitor-related.
Alkylator/radiation therapy-associated AML (t-AML) and MDS (t-MDS) usually develop 4-7 years after receiving the relevant treatment. Approximately 2/3 of patients present with MDS or AML with multilineage pathologic hematopoiesis, often with clinical involvement of chromosome 5 or 7, and have a poor prognosis.
AML associated with topoisomerase II inhibitors Patients in this group often have no significant history of MDS, mononucleosis is often present at the time of AML onset, and exposure to associated topoisomerase II inhibitors has a short time to AML onset of about 6 months to 5 years, with a median of 2-3 years. t-AML is commonly associated with genetic alterations involving balanced translocations of 11q23 or 21q22, but also inv(16) ( The response to chemotherapy and overall survival of patients with this type are similar to those with primary AML with the same genetic abnormality (novo AML).
3.4 Other types of AML
This type of AML mainly refers to those who do not have any of the above types of staging criteria but have ≥ 20% of primary cells in the bone marrow and blood. Considering the existing conditions in most hematology laboratories and the comparability of clinical data evaluation, the classification of this group of patients is still based on the FAB classification, i.e., morphologically based, although the proportion of primary cells for AML diagnosis should be in accordance with the WHO classification. In particular, the following two types should be described:
3.4.1 Acute erythroleukemia
It is also considered to be a heterogeneous disease with malignant red lineage proliferation, especially when there is a predominance of red lineage progenitor cells and little or no myeloid cells, which is not included in the diagnosis of AML in the FAB classification. The type is divided into two subtypes according to the number of myeloid primitive cells in the bone marrow. In some cases, AML with multilineage pathological hematopoiesis may also be diagnosed as The latter is simply diagnosed as “AML with multilineage pathogenic hematopoiesis, acute erythroleukemic”. The other subtype is “pure erythroleukemia”, which is characterized by a bone marrow in which the progenitor cells are limited to the red lineage and comprise 80% or more of the nucleated cells, with a low percentage of myeloid progenitor cells. In some patients, the morphology of the primitive cells is much earlier and it is difficult to determine the nature of the lineage. This type of patient is very similar to the “DiGuglielmo” disease reported in earlier years.
3.4.2 Acute allogeneic myeloproliferative disease with myelofibrosis
This disease is one of the AML with poor prognosis, accounting for about 1%-2% of acute leukemias. It is characterized by an acute course with ≥20% primitive cells in bone marrow and blood, often accompanied by multilineage pathological hematopoiesis, proliferation of promyelocytic (young) megakaryocytes, and myelofibrosis of varying degrees. It is generally considered to be the same disease as acute myelosclerosis, acute myelofibrosis, acute myelodysplastic syndrome with myelofibrosis, or malignant myelosclerosis as reported in the literature. It must be clinically distinguished from primary chronic myelofibrosis, AML with multilineage pathological hematopoiesis and low-grade MDS with myelofibrosis, as well as from acute megakaryocytic leukemia. While the latter is prone to myelofibrosis, the former is a full-blown myelopathy with myelofibrosis.
The diagnostic criteria for each type of AML in the WHO classification
I. AML with specific cytogenetic abnormalities
1. AML with t(8;21)(q22;q22), (AML1/ETO)
AML accounts for 5%-12% of AML; originated from myeloid hematopoietic stem cells with significant differentiation stage to neutrophils; clinically easy to see myeloid sarcoma; cell morphology and histochemical features show that a large number of large leukemic primitive cells are seen in the bone marrow with abundant cytoplasm, basophilic and containing more asplenophilic granules. Auer vesicles were easily seen, often as single elongated granules. These cells often have abnormal nuclear lobulation (e.g., pseudo-Pelger-Huet nuclei) and pink cytoplasm. Immunophenotypes show CD13, CD33, MPO and CD34 expression, often with CD19 co-expression and poor prognosis if CD56 is expressed; cytogenetic examination shows t(8;21)(q22;q22), (AML1/ETO), and if such cytogenetic abnormalities are detected, the diagnosis of AML should be made even if there are less than 20% primitive cells in the bone marrow, rather than MDS-RAEB. MDS-RAEB usually responds better to chemotherapy, has a high remission rate, and has a high long-term disease-free survival rate after consolidation therapy with high doses of Are-C. However, cells that express CD56 or have other additional abnormal chromosomes (e.g., del(9)(q22) or sex chromosome loss) have a poor prognosis.
2. Acute promyelocytic leukemia with t(15;17)(q22;q11~22), (PML/RARa) and variants
It is a clinical complication of diffuse intravascular coagulation (DIC), typically coarse granular and some fine granular, the latter often with hyperleukocytosis, and short cell multiplication time, effective on all-trans retinoic acid (RAR) and arsenic therapy; the cell morphology is abnormal promyelocytosis, the nuclear size and morphology of these cells These cells have irregular nuclei and morphology, increased cytoplasmic granules, and Auer vesicles, which are thick and long, sometimes in the form of bundles. Immunophenotype showed positive CD33 and CD13, but CD34 and HLA-DR were not expressed, and CD2 and CD9 were co-expressed. gene (PML) fused to form PML/RARa, a few patients lacked the typical t(15;17)(q22;q11~22) by conventional chromosomal techniques and showed complex variant translocations involving chromosome 15 or 17; most patients had a better prognosis after combination chemotherapy with RAR, arsenic-inducing differentiation agent containing anthracyclines.
3, AML with bone marrow abnormal eosinophils and inv(16)(p13;q22) or t(16;16)(p13;q22), (CBFβ/MYH11)
Myeloid sarcoma may be present at the time of diagnosis and relapse, and is sometimes the only evidence of relapse; cytomorphology shows that in addition to the features of acute granulocytic leukemia, abnormal eosinophils are seen in the bone marrow at all stages, with large, coarse, purple eosinophil granules, which are seen in early and middle-aged granulocytes, and mature eosinophils lacking lobulation; immunophenotype The immunophenotype showed that in addition to expressing myeloid antigens (CD13, CD33, MPO), they often expressed monocyte antigens (CD14, CD4, CD11b, CD11c, CD64, CD36 and lysosomes) and co-expressed CD2; cytogenetic examination showed that inv(16)(p13;q22) or t(16;16)(p13;q22), both of which could lead to fusion of CBFβ gene on 16q22 with MYH gene on 16p13; better response to chemotherapy, higher remission rate and long-term disease-free survival rate after treatment containing high dose of Are-C.
4, AML with 11q23 (MLL)
Approximately 5%-6% of AML, although seen in all age groups, but mostly in children or infants, occasionally seen after topoisomerase II inhibitor treatment; originates from hematopoietic stem cell stage with multidirectional differentiation; clinically prone to DIC, page may have extramedullary monocyte sarcoma or tissue infiltration (gingiva and skin); 11q23 abnormalities are closely related to acute monocytic or granulocytic leukemia, promyelocyte Monocytes have large cytosomes, abundant cytoplasm, basophilic staining, pseudopods, scattered fine asplenophilic granules, and vacuoles and larger nuclei often with one or more nucleoli, and often negative MPO. Young monocytes have irregular cytosomes, folded nuclei, basophilic cytoplasm, often with granules, occasionally large aspergillus granules and vacuoles, monocytes are strongly positive for nonspecific esterases, which are inhibited by sodium fluoride; immunophenotype shows CD34- and positive for granule/monoclinic antigens (CD13, CD33, CD4, CD14, CD11b, CD11c, CD64, CD36 and lysosomes); molecular Molecular examination can be expressed by HRX and MLL genes, but also t(9;11(p21;q23), t(11;19)(q23;p13), t(11;19)(q23;p13.3) translocation; its prognosis is fair, intermediate level.
Second, AML with multilineage pathological hematopoiesis
1. History of MDS or MDS/MPD
The disease refers to ≥ 20% of primitive cells in bone marrow or blood before treatment, and ≥ 2 lineages of pathological hematopoiesis, pathological cells account for more than 50% of each lineage, usually involving megakaryocytic lineage. It may be primary (de novo) or have a history of MDS/MPD, mainly in elderly patients; clinically there is often severe allogeneic cytopenia; the cytomorphological or cytochemical features are similar to those of MDS; immunophenotypic examination has CD34+ and other markers of allogeneic cells (e.g., CD13, CD33, etc.), often expressing both CD56 and/or CD7, and multidrug resistance protein ( The cytogenetic alterations are similar to MDS, often with the acquisition and loss of certain major chromosomal segments, such as -7/del(7q), -5/del(12p), +8, +9, +11, del(11q), del(12p), -18, +19, del(20q), +21, and a few with more specific chromosomal translocations (e.g. t( 2;11), t(1;7) and translocations involving 3q21 and 3q26, abnormalities in the 3q26 region (e.g., inv(3)(q21q26), t(3;3)(q21;q26), ins(3;3)) often with thrombocytosis, inv(3)(q21q26) often with bone marrow megakaryocytosis, t(3;2)(q21;q26) often with treatment-related or acute changes in CML, while t(3;5)(q25;q34) is not associated with thrombocytosis. This type of AML responds poorly to chemotherapy, and its prognosis is poor.
2. Treatment-related AML and MDS
The occurrence of this type of AML is due to previous chemotherapy/radiotherapy and is classified according to the cause:
2.1 Alkylator-associated AML/MDS occurs mostly after 5-6 years (10-192 months) of receiving alkylators and radiotherapy, and the risk factors for its occurrence are closely related to the cumulative amount of drugs used and the age of the patient.
Topoisomerase II inhibitor-associated
Other types
Other types of AML (those who do not fit the above types)
AML, minimally differentiated
AML, immature
AML with maturation
Acute monocytic leukemia (AMML)
Acute monocytic leukemia
Acute red leukemia (erythroleukemia/leukemia and pure red leukemia)
Acute megakaryocytic leukemia
Acute basophilic leukemia
Acute panmyelosis with myelofibrosis
Myeloid leukemia sarcoma