**ABBREVIATIONS USED:**

**AML WITH RECURRENT GENETIC ABNORMALITIES**

30% of cases of AML. AML t(8;21) = Acute myeloid leukemia with t(8;21), AML inv(16) or t(16;16): Acute myeloid leukemia with inversion or translocation chromosome 16 and abnormal marrow eosinophils, APL : Acute promyelocytic with t(15;17), APL-M: Acute Promyelocytic leukaemia, microglandular or hypogranular variant, AML t(9;11): Acute myeloid leukemia with t(9;11q23), AML t(6;9): acute myeloid leukaemia with t(6;9), AML inv(3) or t(3;3): Acute myeloid leukemia with inversion or translocation chromosome 3, AML t(1;22): acute myeloid leukaemia megakaryoblastic, AML NPM1: Acute myeloid leukemia with mutated NPM1, AML CEBPA: Acute myeloid leukemia with mutated CEBPA

**AML PRESENTING OR ASSOCIATED WITH MYELODYSPLASIA**

AML with MDS: acute myeloid leukaemia with MDS related changes, MDS/MPN changes, MDS related cytogenetics, abscense of specific genetic abnormalities of AML and no history of radiation or chemotherapy (See .Differential Diagnosis for discussion),

t-AML/t-MDS/MPN: therapy related acute myeloid leukaemia/myelodysplastic syndrome/myeloproliferative neoplasm.

**AML NOS or AML not otherwise specified** (Cases classified before chemotherapy not fulfilling criteria for previous groups based in >20% blasts count in smears or CD34 stains in biopsy, and morphologic/cytochemistry FAB classification. Patients may have complex karyotype but no unique chromosomal abnormalities. Abbreviations for this category: AML w MD (Acute myeloid leukaemia with minimal differentiation), AML without M (Acute Myeloid Leukaemia without maruration), AML w M (Acute myeloid leukaemia with maturation), AMML (acute myelomonocytic leukaemia), A Monoblastic (acute monoblastic), A Monocytic (acute monocytic), EL (Erythroleukemia), PEL (Pure erythroid leukaemia), A Mega (Acute Megakaryoblastic), A Baso (Acute Basophilic Leukaemia)

**Main References consulted:**

Wikipedia

eMedicine

WHO classification of tumors of hematopoietic and lymphoid tissues

AFIP Bone marrow atlas of pathology

Other multiple sources.

Last reviewed 9/301/2010

**AGE AND INCIDENCE**

Most acute leukemias possible in all ages.

t-AML/t-MDS/MPN post alkylating is possible at any age, more common than t-AML/t-MDS/MPN post topoisomerase II, more common in older

Different peaks: AML t(6;9) peak around puberty and a second peak around 3th decade. AML w MD peak in kids and older.

More common in younger or kids: AML t(1;22) in infants < 3 y/o, AML t(8;21), AML inv(16), AML t(9;11), AML with Down Syndrome.

Common in adults/mid life: APL, AML without M, EL

Common in older: AML with MDS changes, , t-AML/t-MDS/MPN post topoisomerase, AMML

Leukemias considered very rare in incidence (<2% of cases): AML t(6;9), AML inv(3) or t(3;3), AML t(1;22), A Baso,

**CELL OF ORIGIN**

Hematopoietic Stem Cell: AML NPM1, AML CEBPA, AML with MDS, t-AML/t-MDS/MPN, all cases of AML NOS

Myeloid Stem Cell with granulocytic differentiation: APL , APL-M

Myeloid Stem Cell Neutrophil differentiation: t(8;21)

Myeloid Stem Cell Neutrophil and monocytic differentiation: inv(16) and t(16;16)

Myeloid Stem Cell megakaryocytic differentiation: AML t(1;22)

Multilineage potential: t(6;9), AML inv(3) or t(3;3) .

**CLINICAL PRESENTATION, OTHER SITE INVOLVED ADDITIONAL TO MARROW**

Most bone marrow failure with infection due to neutropenia, anemia, thrombocytopenia, weakness and leucocytosis. Bleeding very common in A Monoblastic and A Monocytic.

Hepatosplenomegaly: Most AML t(1;22) and A Baso. Some AML inv(3) or t(3;3). Rarely in A Mega.

DIC : APL, AML t(9;11)

CNS: Common in A Monoblastic and A Monocytic.

Adenopathy: AML NPM1. Rare in AML inv(3) or t(3;3). Very rare in other.

History of cytotoxic or radiotherapy:

In t-AML/t-MDS/MPN postalkylating , 5-10 years post chemo patient appears with t-MDS (dyserytropoiesis with increase in ring sideroblasts, dysgranulocytopoiesis and dysplastic megas) or myelomonocytic leukaemia. Slowly (years later) evolves a overt t-AML.

In t-AML/t-MDS/MPN post topoisomerase II 1-5 years post chemo patient appears with overt leukaemia without previous MDS or myelomonocytic leukaemaia.

AML with MDS is not related with drugs or radiotherapy.

Myeloid Sarcoma or tumors in extramedullary lesions other than BM (skin, GIT, gingiva, bone, soft tissues, testis etc): May be initial manifestation or indication of relapse. It is not necessarily a bad px factor and patient still may be cured. Common origin in monoblastic ( A Monoblastic, A Monocytic , AMML) and granulocytic. Also seen in AML t (9;11), AML NPM1, AML t(8;21), inv(16), t(16;16) and others. Genetic abnormalities associated with MDS may be present if the case is a blastic transformation of MDS.

CD34, CD117 and markers for granulocytic and monocytic lineage may be +. Erythroid, mega and aberrant lymphoid differentiation is very uncommon ( rarely mega markers as CD61 or erythoid markers as glycophorin are positive). Skin involvement and lytic bones are findings very common in A Baso

**PERIPHERAL BLOOD (PB) AND LAB FINDINGS**

WBC count :

Moderate increase in WBC count in most. Higher count seen in AML NPM1. Very high in APL-M.

Low WBC count average 12K in AML t(6;9).

Manual differential and morphology of leucocytes:

Circulating blasts possible in most. APL only rare ciruculating promyelos.

Monocytosis in AML inv(16) or t(16;16) and someAML w M. Marked monocytosis required for dx of AMML (5 x 109 /L ) with most mature monocytes, A Monocytic and A Monoblastic.

Increase in eos in many AML inv(16) or t(16;16) and AML inv(3) or t(3;3). Commonly increased in AML t(8;21) and AML w M

Abnormal hyposegmented eos: AML inv(16) or t(16;16)

Basophilia common in AML t(6;9), AML inv(3) or t(3;3), A Baso, AML w M, t-AML/t-MDS/MPN post alkylating in the phase of MDS and overt leukaemia and some AML t(8;21),

Dysplasia in granulocytes: AML t(6;9), inv(3) or t(3;3) pseudopelguer huet with hypogranular PMNs. Cases of AML with MDS. Some AML t(8;21) abnormal with pink cyto, subset of AML NPM1, t-AML/t-MDS/MPN related with alkylating drugs, AML w M

Hb : Low in many AML. Very common in AML t(6;9) and inv(3) or t(3;3). High in AML CEBPA

Thrombocytopenia: many AML. Very common in AML t(6;9) and AML t(1;22).

Thrombocitosis: highest count of all in AML NPM1. Common in AML inv(3) or t(3;3). Rarely in A Mega (more commonly thrombocytopenia).

Platelet morphology: Occasional giant hypogranular platelets in AML inv(3) or t(3;3).

Other labs:High LDH in AML CEBPA

**BONE MARROW (BM) ASPIRATE**

**Number of blasts, neutrophils, monocytes and precursors:**

For all cases of AML NOS >20% blasts required.

Highest count of blasts seen in AML NPM1

If myeloid sarcoma 20% threshold not required.

Some cases of AML with recurrent genetic abnormalities dx is possible with < 20% blasts. AML t(8;21) or inv(16) or t(16;16) or t(15;17) are AML even if BM < 20%

Monitor for definitive evidence of AML if blasts < 20%: AML t(6;9), AML inv(3) or t(3;3), AML t(1;22) and AML with MDS.

AML t(1;22) with <20% blasts: may be due to dry aspirate due to common marrow fibrosis

AML w M: >20% blasts but >10% are promyelos, myelos and PMN and <20% monocytic lineage.

AMML: >20% blasts (including promonocytes that are blasts equivalents), neutrophils and precursors > 20%, monocytes and precursors >20%.

A Monoblastic: > 80% monoblasts <20% neutrophilic component

A Monocytic: > 80% monocytic (most promonocytes). < 20% neutrophilic component

EL: > 50% erythroid precursors in all nucleated cells and >20% myeloblasts (% of nonerythroid cells).

PEL: > 80% marrow cells are proerythroblasts.

A Mega: >20% blasts with at least 50% megakaryoblasts.

**Blasts morphology: **

AML t(8;21) large blasts with abundant basophilic granular cyto with clearing hofs.

APL: Most promyelos with kidney shape, purple granules and auer rods, but some myeloblasts with auer rods.

Blast is kidney shaped with convoluted nuclei and cyto packed with granules (if basophilic cyto suggest ATRA treatment).

AML t(9;11): Monoblasts (round nuclei, big nucleoli and abundant basophilic cyto with pseudopods) + promonocytes (convuoluted nuclei with granulated cyto and azurophilic granules).

AML t(6;9): any FAB morphology (except APM or megakaryoblastic). Most common morphology is AML with maturation and acute myelomonocytic.

AML inv(3) or t(3;3): any FAB morphology (except APM). Most common AML with maturation, acute myelomonocytic or megakaryoblastic. Rare cases look like CMML.

AML t(1;22) megakaryoblasts measuring 12-18 microns with indented nuclei, nucleoli, basophilic cyto and blebs. Mixed with blasts resembling lymphoblasts. Micromegas are present.

AML NPM1: 90% of acute monocytic are NPM1 +, many have acute myelomonocytic morphology and some AML with or without maturation or acute erythroid leukemia.

AML CEBPA: Most AML with or without maturation morphology. Some myelomonocytic or monoblastic.

t-AML/t-MDS: Acute leukemia appears after years with typical marrow of MDS

t-AML/t-MDS/MPN : if balanced translocation is t(9;11) behaves as monoblastic. If t(8;21) blasts with basophilic granular cyto, if (15;17) promyelos and if t(4;11) behaves as ALL. Other translocations possible.

**AML NOS: **

AML w MD: Medium side round blasts with no granules or rarely small blasts simulating ALL.

AML without M: Myeloblasts with some azurophils granules or Auer rods. Sometimes small resembling lymphoblasts.

AMML vs A Monoblastic vs A Monocytic: Look for mixtures of monoblasts and promonocytes in AMML. Nuclei round in monoblast with one or more nucleoli. Nuclei convoluted or lobulated in promonocytes. Cyto more basophilic in monoblast with pseudopod. More obvious azurophilic granules and vacuoles in promonos.

EL: myeloblasts are immature like AML without maturation. Erythroid cells seen in all stages of maturation with dysplasia and vacuoles.

PEL: Pure erythroblasts: medium to large size, round nuclei, one or more nucleoli, basophilic agranular cyto and vacuoles.

A Mega: Megakaryoblasts have round nuclei, one to 3 nucleoli, cyto basophilic agranular PAS+ with pseudopode and clusters are common. Micromegas have 2 round condensed nucleoli, mature cyto and should not be counted as blasts.

A Baso: round or bilobed nucleus and coarse basophilic granules.

**Positive granules:**

Some azurophils granules may be seen in AML without maturation. They are easily identified in some blasts in AML w M, AMML and A Monocytic, specially in promonos (granules more prominent and larger than monoblasts)

Numerous azurophilic granules in blasts in AML t(8;21)

Numerous large eosinophilic granules that obscure morphology in promyelos and myelos in AML inv(16) or t(16;16).

Numerous large purple red granules and some blasts that obscure morphology in promyelos and myelos in APL. APL-M only submicroscopic granules with hypogranular cytoplasm (except some promyelos with visible granules).

Coarse basophilic granules: A Baso.

**Auer Rods :**

Classically in APL.

Common: in AML t(8;21) in blasts and some neutrophils and AML w M

May be seen: AML inv(16) or t(16;16) and AML t(6;9),

Present in some blasts and promyelos in APL and APL-M

**Blasts with perinuclear clearing or hofs: AML** t(8;21)**Blasts with very large granules (pseudo Chediak-Higashi):** AML t(8;21),**Abnormal number of neutrophils: **Decreased in AML inv(16), t(16;16)**Dysplasia in neutrophils/dysgranulocytopoiesis** (pseudo pelguer huet nuclei with hypogranular cyto or bizarre segmentation in PMNs): AML t(8;21), AML t(6;9), inv(3)/ t(3;3), many cases of AML with MDS, subset of AML NPM1 show dysplasia, t-AML/t-MDS/MPN related with alkylating drugs, AML w M, EL, A Mega. If pink cyto may be AML t(8;21)**Abnormal number or morphology in eosinophils:**

Commonly Increased number with nnormal morphology in AML t(8;21), AML inv(16), t(16;16) , AML inv(3) or t(3;3) and AML w M

Increased number with abnormal morphology (hyposegmented eos) in AML inv(16) or t(16;16)

Erythroid dysplasia (dyserythropoiesis): Very common in EL that commonly evolves from MDS or MPN showing red blood cells precursors with megaloblastoid nuclei, bi or multinucleation and coalescing cytoplasmic vacuoles. Erythorid dysplasia also present in AML t(6;9), inv (3) or t(3;3), subset of AML NPM1, many cases of AML with MDS, t-AML/t-MDS/MPN related with alkylating drugs, A Mega.

Erytrophaghocytosis: Some cases of A Monoblastic and AML w M, both related with t(8;16)

**MARROW BIOPSY**

Cellularity: Normo to hypercellular. Markedly hypercellular in AML NPM1

Number of megakaryos: Increased in AML inv(3) or t(3;3) and may be increased in AML with MDS and t-AML/t-MDS/MPN

Dysplastic megakaryos: Biosy is better tha aspirate to see dysplasia of megas. Present in many AML t(1;22), EL, AML inv(3) or t (3;3), AML with MDS and t-AML/t-MDS/MPN related with alkylating drugs, A Mega. Subset of AML t(6;9) and AML NPM1.

Reticulin fibrosis: Essential for dx due to possibility of dry tap biopsy. Seen in some cases of AML inv(3) or t(3;3), many AML t(1;22) and A Mega

**IMMUNOHISTOCHEMISTRY AND FLOW CYTOMETRY**

**MYELOID OR GRANULOCYTIC ASSOCIATED ANTIGENS**

CD13: Myeloid associated antigen. Most: AML t(8;21), granulocytic population of AML inv(16) or t(16;16), AML t(6;9), AML inv(3) or t(3;3), AML NPM1, t-AML/t-MDS/MPN related with alkylating drugs, APL (positive heterogeneous). Common: AML t(1;22), AML CEBPA, AML with MDS, AML w MD, AML without M, AML w M, AMML, A Monoblastic and A Monocytic, A Baso. Weak : AML t(9;11) in kids. Negative: A Mega

CD15: Marker of Granulocytic maturation. Most: granulocytic population of AML inv(16) or t(16;16). Common: subpopulation of AML t(8;21), AML CEBPA, AML w M, AMML, A Monoblastic and A Monocytic.. Negative or weak: APL. Negative: AML w MD, AML without M.

CD33: Myeloid associated antigen Most: granulocytic population of AML inv(16) or t(16;16), APL, AML t(9;11) in kids, AML t(6;9), AML inv(3) or t(3;3), t-AML/t-MDS/MPN related with alkylating drugs, Common: AML t(1;22), AML CEBPA, AML with MDS, AML w MD, AML without M, AML w M, AMML, A Monoblastic and A Monocytic (bright), A Baso. Weak: AML t(8;21) Negative: A Mega

CD65: Marker of granulocytic maturation. Most : granulocytic population of AML inv(16) or t(16;16), AML t(9;11) in kids Common: subpopulation of AML t(8;21), AML CEBPA, AML w M, AMML, A Monoblastic and A Monocytic. Negative or weak: APL. Negative: AML w MD, AML without M,

CD117: Myeloid associated antigen. Most AML inv(16) or t(16;16), AML without M, AML w MD Common: AML w M, AMML is positive in immature blasts, erythroblasts in EL and PEL. Weak AML t(9;11) in kids and adults, APL Negative: A Baso

MPO : Specific myeloid marker. Most: AML t(8;21), positive in granulocytic population of AML inv(16) or t(16;16), AML NPM1 and myeloid sarcoma with granulocytic lineage. AML w M show numerous blasts MPO positive. AML withouth maturation + in >3% blasts. Myeloblasts in EL stains as AML without M (> 3% positive for MPO). Although AML w MD is negative by cytochemistry, some blasts may be positive by IHC. In A Monocytic MPO is positive in promonocytes. Negative: Most monoblasts in A Monoblastic, erytroblasts in EL and PEL, A Mega.

**MARKERS OF MONOCYTIC DIFFERENTIATION**

CD4: Most: monocytic population of AML inv(16) or t(16;16), AML t(9;11) in kids and adults. Common: AMML, A Monoblastic and A Monocytic. Rare or negative: AML w M.

CD11b: Most: monocytic population of AML inv(16) or t(16;16) Common: AML t(9;11) in adults, AML CEBPA, AML w M, AMML, A Monoblastic and A Monocytic, A Baso. Negative or weak: APL, AML w MD, AML without M.

CD11c: Common : AML inv(16) or t(16;16) in monocytic population, AML t(9;11) in adults, AMML, A Monoblastic and A Monocytic

CD14: Most: monocytic population of AML inv(16) or t(16;16), AML NPM1. Common: AML t(9;11) in adults, AML CEBPA, AMML, A Monoblastic and A Monocytic.. Weak : AML t(9;11) in kids. Negative: AML w MD, AML without M, AML w M.

CD36: Most: AML t(1;22), monocytic population of AML inv(16) or t(16;16). Common: AML t(9;11) in adults, AMML, A Monoblastic and A Monocytic.

CD64: Most: monocytic population of AML inv(16) or t(16;16). Some: APL, AML t(9;11) in adults, AML CEBPA, AMML, A Monoblastic and A Monocytic, AML t(6;9) Negative: AML w MD, AML without M, AML w M.

CD68: Common: AMML, A Monoblastic and A Monocytic, myeloid sarcoma.

CD123: A Baso

CD203: A Baso

CD163: Common: AMML, A Monoblastic and A Monocytic.

Lysozyme: Most: monocytic population of AML inv(16) or t(16;16). Common: AMML, A Monoblastic and A Monocytic.

**LYMPHOID MARKERS**

cCD3: Specific T cell marker. Negative: AML w MD, AML without M.

CD7: Some: AML with MD, AML without M, AML w M, AMML, A Monoblastic and A Monocytic, AML CEBPA, AML with MDS, AML w MD, AML inv(3) or t(3;3), t-AML/t-MDS/MPN. Rare: A Mega

cCD22: Specific B cell marker . Negative: AML w MD, AML without M

CD19: Specific B cell marker. Common: AML t(8;21) Rare: AML without M, AML w M.

cCD79a: specific B cell marker. Common: AML t(8;21) Negative: AML w MD, AML without M.

**MEGAKARYOCYTIC MARKER**

CD41: Most: a Mega (cytoplasmic). If membranous nor reliable, may be adhered platelets. AML t(1;22) Common: AML inv(3) or t(3;3) Negative: PEL and EL

CD42: Some: AML t(1;22)

CD61: Some: AML inv(3) or t(3;3) Negative: PEL and EL Most: Mega, AML t(1;22) + in cyto (membranous not reliable may be due to adhesed platelets).

**ERYTHROID MARKERS**

Hemoglobine A: erythroid precursors in EL and PEL. IHC very useful in biopsy.

Glycophorin: erythroid precursors in EL and PEL, except very immature forms in PEL. IHC very useful in biopsy.

**OTHER**

CD2: Common: AML inv(16) or t(16;16), APL-M. Rare: AML without M, AML w M.

CD9: Most: A Baso

CD11a: Negative or weak: APL, Rare: AML without M.

CD18: Negative or weak: APL

CD22: Some: A Baso.

CD23/nucleolin by IHC: nuclear stain positive in AML NPM1

CD25: Negative: A Baso

CD34: Most: AML t(8;21), inv(16), t(16;16), APL-M, AML inv(3) or t(3;3), t-AML/t-MDS/MPN , AML w MD, AML without M. Weak : AML t(9;11) in kids Rare: A Mega, A Monoblastic and A Monocytic (only positive in 1/3) Negative or weak: APL. Negative: AML NPM1, erythroblasts in EL and PEL.

CD36: Proerythroblasts in PEL. It is not an specific erythroid marker.

CD38: AML t(6;9), AML inv(3) or t(3;3), AML w MD

CD45: Negative: AML t(1;22), CD45

CD56: Marker of bad px. Common: AML t(8;21), some cases of APL, AML t(9;11) in adults, AML with MDS, t-AML/t-MDS/MPN, EL. Rare: AML without M, AML w M, A Monoblastic and A Monocytic

CD123: Positive: Myeloid Sarcoma with plasmacytoid dendritic cell differentiation carrying inv(16).

TdT: Negative: AML t(1;22), A Mega weak AML t(8;21). Some: AML t(8;21), AML t(6;9), AML w MD, A Baso.

HLA-DR: Most in AML t(8:21) , AML t(9;11) in kids, AML t(6;9), AML inv(3) or t(3;3), AML w MD, AML without M, AMML . Common: AML CEBPA, AML w M, A Monoblastic and A Monocytic, A Baso. Rare: APL (HLA-DR expression does not support APL), AML t(1;22) , A Mega, erythroblasts in EL and PEL.

PAX5: Common: AML t(8;21).

Tryptase: Negative: A Baso

**CYTOCHEMISTRY**

Naphthol-ASD-chloroacetate esterase (CAE) is a granulocytic stain

Positive: AMML. AML inv(16) or t(16;16) faint in abnormal hyposegmented eos, myeloid sarcoma with granulocytic lineage

Negative: AML t(8;21), AML w MD, A Mega, A Baso

Non-specific estearase ( alpha naphthyle acetate and butyrate estearases) is a monocytic stain

Positive: Most AML t(9;11) and PEL. Many AMML, A Monoblastic and A Monocytic wit intense + in monoblasts and promonos. AML inv (16) or t(16;16) weekly positive in monoblasts and promonos, myeloid sarcoma with monoblastic lineage.

Variable: AML t(6;9)

Weak : APL weak. A Mega may be punctate and focal, non specific.

Negative: A Baso. Rare negative cases of NSE in AMML and A Monoblastic does not exclude dx.

MPO or Sudan Black is a granulocytic stain

Positive: In APL MPO strongly + in all promyelos. AML t(6;9), AML NPM1, at least 3% blasts in AML inv(16) or t(16;16) and AML CEBPA. AML w M show numerous blasts MPO positive. AML without M and AMML require positivity in > 3% of blasts. Rare monoblasts and common promonocytes may be positive in AMML. MPO is generally negative in A Monoblastic and it is only weak or scatterly positive in promonocytes in A Monocytic. Myeloblasts in EL are MPO/Sudan +. MPO/Sudan is + in Myeloid sarcoma with granulocytic origin.

Negative: AML t(1;22), AML t(9;11), aML w MD and A Mega. A Baso is neg. Proerythroblasts in PEL and Erytroblasts in EL are MPO/Sudan negative.

Doble staining NSE and CAE or MPO

Clue for dx of AMML

PAS

PAS + single vacuoles, coalescing or diffuse seen in EL, PEL, A Mega and focally in A Baso.

Metachromatic (toloudine blue):

A Baso**CYTOGENETICS AND MOLECULAR**

AML t(8;21) involves AML1 gene and ETO. KIT mutations in some cases

Both AML inv(16) and t(16;16) fusion CBFB ans MYH gene that if not detected by conventional cytogenetics is detected with FISH or PCR. Other additional: 22+ and KIT mutation.

APL t(15;17) between PML-RARA. APL lacking t(15;17) may have submicroscopic or cryptic t(15;17). Some variants of RARA translocation described as t(11;17).

APL-M FLT3-ITD mutations and bcr3 breakpoint of PML-RARA. RARA is Retinoic acid receptor in chromo 17 that may be treated with ATRA.

AML t(9;11): translocation between MLLT3 and MLL, with 11q23 abnormalities, not related with chemotherapy. Other rare MLLT translocations described as MLLT-1, MLLT3, MLLT4 and MLLT10 are related with AML with myelomonocytic or monoblastic features, and commonly only detected by FISH. MLLT2 related with ALL. |

AML t(6;9) fusion of DEK on chromo 6 with NUP214 on 9. Very uncommon mutations of FLT3-TDK

AML inv(3) or t(3;3): MDS1-EVI1 and RPN1. Rarely monosomy 7 and 5q deletions. Some CML in Acelerated phase adquire inv(3).

AML t(1;22): RBM15-MLK1 fusion

AML NPM1: Karyotype is normal. IHC look for cytoplasmic expression of NPM and CD23/nucleolin by IHC looking for nuclear stain positive in AML NPM1. Some carry FLT3-ITD.

AML CEBPA: CEBPA mutation with normal Karyotype. Some associated with FLT3D mutation.

AML with MDS: See Differential Diagnosis below .

t-AML/t-MDS/MPN post alkylating drugs: Unbalanced loss 5 and 7 + some additional

t-AML/t-MDS/MPN post topoisomerase II: Balanced translocations: common t(9;11) and t(8;21). Rare t(15;17) and t(4;11). Other translocations possible.

Other additional genetic mutations in AML with normal cytogenetics, detected only with FISH or molecular tests:

FLT3-ITD, MLL-PTD, Cytoplasmic NPM, NPM1, CEBPA, WT-1, ERG expression, MN1 expression, BAALC expression

AML NOS:

No unique chromosome abnormality in any subtype.

Complex or non specific karyotype abnormalities present in some cases like AML w MD and AMML, EL and PEL

If EL and PEL specific abnormalities associated to MDS like del5, del 7 or 8+, classify better as AML with MDS.

If erytrophagocytosis present in AML w M, AMML, A Monoblastic or A Monocytic is related with t(8;16)

A Mega not include t(1;22), t(3;3) or AML with MDS (see differential dx below).

Cases of A Mega reported in young male with mediastinal germ tumors and 12p

A Baso: Nothing characteristic. Exclude t(6;9) also related with basophilia.

**DIFFERENTIAL DIAGNOSIS**

AML with MDS: It is very common, and may correspond to 1/3 of all AML. Include cases with :

No prievious history of radiation or chemotherapy.

No specific genetic abnormalities of AML

Acute myeloid leukaemia with MDS morphologic changes (dysgranulopoiesis, dyserytropoiesis and dysmegakaryopoiesis)

AML with MDS related cytogenetics : -7, -5, and other rare: t(3;5), t(2;11) or t(11;16). Do not confuse AML with MDS with t-AML/t-MDS/MPN , always related with alkylating drugs or topoisomerase II.

AML with MDS/MPN morphologic or genetic changes

AML with multilineage dysplasia with abnormal karyotype and NPM1, CEPBA and or FLT3.

Do not include distinct entities as: AML inv(3) or t(6;9) with multilineage dysplasia

Therapeutic decisions for MDS related AML should be based on clinic, evolution, history of previous growth factors and genetic data (not on blast percentage).

Principal differential dx or AML with MDS: Refractory anemia with excess of blasts, AML or AML NOS related with multilineage dysplasia or genetic changes as monosomy 7. If EL suspected but dysplasia in >50% of cells in 2 lineages, dx is AML with MDS.

AML t(1;22) may imitate metastatic tumors if collagen fibrosis marked.

AML NOS:

AML w MD: differential with Acute Megakaryoblastic Leukaemia and ALL if blasts small.

AML without M: ALL if blasts small or AML w M if high % of MPO + blasts.

AML w M: If low number of blasts careful with RAEB because dysplasia is frequent. If increased monocytes may be confused with myelomonocytic leukaemia.

EL: diff with RAEB, AML with MDS or AML treated with erythropoietin

PEL: If megaloblastic anemia suspected trial of B12 or folate recommended. Differential with A Mega is based in immunophenotype.

A Mega: Megakaryoblastic crisis in Myeloproliferative Neo (look for chronic presentation with hepatospleno in MPN).

Acute Panmyelosis with myelofibrosis is very difficult differential but all 3 series are affected, not only megas.

A Baso: Mast cell leukaemia is CD25+ and CD117+, AML t(6;9) also basophilia.

Myeloid Sarcoma: Lymphoblastic Lymphoma, Burkitt, DLBCL,small round cell tumors and blastic plasmocytoid dendritic cell neo.

ALL: For differential diagnosis and information about precursor lymphoblastic lymphoma/leukaemias, go to molecular genetics in hematologic neoplasias and read under the chapter of FISH: Precursor Lymphoid Neoplasias.

**EVOLUTION/PROGNOSIS**

Long survival and/or good response to chemo:

AML t(8;21), inv(16), t(16:16). If AML inv(16) or t(16;16) has 22+ good px.

APL and APL-M better px than other leukemias treated with ATRA/arsenic.

AML t(1;22)

AML NPM1 (cytoplasmic NPM), comparaable to AML t(8;21)

AML CEBPA may improve px in some cases, comparable with AML t(8;21) and inv(16). Px may be not as good if associated FLT3-ITD mutation.

Cases with AML with MDS clearly arising from previous MDS or in kids are slowly progressive and not very aggresive

AML inv(16) or AML t(16;16) no differences in px, they have the same behavior and morphology.

Intermediate px

AML t(9;11q23), better than other AML with 11q23 translocations.

Poor px or shorter survival:

Most cases of AML with MDS

Positive CD56 expression.

Mutation of KIT in AML t(8;21) and AML inv(16) or t(16;16) worse px.

FLT3-ITD mutations. If AML NPM1 carry FLT3-ITD px is worse.

AML with multilineage dysplasia with abnormal karyotype and NPM1, CEPBA and or FLT3. It is not clear if in these cases NPM1, CEPBA and or FLT3 confers some better px.

MLL-PTD

AML inv(16) or t(16;16) with KIT mutation

AML t(6;9) worse if high WBC count or high % of blasts.

AML inv(3) or t(3;3)

WT-1 mutations

ERG expression, MN1 expression, BAALC expression

Most cases of AML with MDS

t-AML/t-MDS/MPN. All bad px but is worse in cases related with alkylating and chromosome 5/7 than topoisomerase II and balanced translocations.

EL and PEL

**OTHER RARE OR RELATED ENTITIES**

**ACUTE UNDIFFERENTIATED LEUKAEMIA: **

All specific markers negative: cCD3 neg (T marker), MPO neg (myeloid), cCD22/cCD79a/CD19 (B cell markers), megakaryocytic markers and plasmocytoid dendritic cell markers. Positive for Blast markers (34, 38, TdT and HLA-DR). May exhibit rarely some B or T cell markers, but not specific.

**MIXED PHENOTIPIC ACUTE LEUKAEMIA:** All very rare and with poor px

**With MLL rearranged:** combine monoblasts and proB phenotype blasts (19+, 10+, 15+, 79a+ and weak 22). FISH detects t(v;11q23). Do not include cases with deletion 11q23.

**With t(9;22):** combine myeloid + lymphoid blasts, most B phenotype. BCR-ABL detected by FISH. Do not include CML with blastic crisis. Imitimab may be useful.

**B/Myeloid NOS:** combine myeloid (13+, 33+, 117+) and lymphoid blasts, B phenotype. No specific genetic.

**T/Myeloid NOS:** combine myeloid (13+, 33+, 117+) and lymphoid blasts, T phenotype. No specific genetic.

**ACUTE PANMYELOSIS WITH MYELOFIBROSIS**

Patient with pancytopenia, fever, bone pain, marrow reticulin fibrosis (dry tap) and no splenomegaly. Blood smear shows macrocytosis (no tear drops or anisopoikylo). Biopsy key to count blasts CD34+ and MPO neg (+ 20%). Myeloid cells are increased (13, 33 and 117+). Megas dysplastic and increased ( CD61, 42b and 41+). Erythroid population increased glycophorin +. Do not count increased micromegas as blasts. Genetic is not characteristic. Do not include specific genetic alterations (for example, del 5 and 7 suggest AML with MDS). Differential dx: other entities wit fibrosis like MPN (more megas and more clustering ), AML with MDS and RAEB-F ( not related with acute fever and bone pain).

**BLASTIC PLASMOCYTOID DENDRITIC CELL NEOPLASM**

Lymphoblasts like cells in marrow and peripheral blood. Skin nodules, plaques and adenopathies. Cells + for : CD4, 123 (dendritic cell marker), TCL-1 (cutaneous lymphocytic marker) and some for 68, 56, TdT and other lymphoid or myeloid markers. Cytotoxic marker TIA1 is negative. This entity is considered in the chapter of leukaemias because has multilineage potential and some cases are related with AMML.

**MDS/ACUTE MYELOID LEUKAEMIA WITH DOWN SYNDROME**

Disorder with hepatospleno related with triso 21, encoding factor GATA1, presenting beyond neonatal period. In neonatal period, probably is Transient Abnormal Myelopoiesis, disorder with similar clinic, morphology and phenotype, high rate of remision and evolution to AML in first 3 years of life. Blasts are most megakaryoblastic. No biological difference between MDS and AML. Cases with refractory cytopenia of childhood with macrocytosis, thrombocytopenia and no increase in blasts are considered same entity that AML (it is just preleukemic phase). Peripheral blood show macrocytosis, anisopoikylo, thrombocytopenia, giant platelets, dyserytropoiesis, dysgranulocytopoiesis, dysplastic megas with micromegas, in clusters. Blasts are positive for: 117, 13, 33, 7, 41, 42, 4, 61 and 71. Negative for: MPO, 15, 14, glycophorin A. Transient myelopoiesis is CD34 and 56+. Only 50-70% of AMS with Down are CD34+ and 56+