Chapter 4: Acute Myeloid Leukemias (AML)

· AML with recurrent genetic abnormalities

· AML with multilineage dysplasia

· AML and MDS, therapy-related

· AML not otherwise categorized

· Acute leukemia of ambiguous lineage

AML with recurrent genetic abnormalities

· t(8;21)(q22;q22)(AML/ETO)

· inv(16) or t(16;16)(p13q22); (CBFβ/MYH11)

· t(15;17)(q22;q21)

· 11q23(MLL)

AML with multilineage dysplasia

· AML plus dysplasia

· Dysplasia: >50% of cells of 2 or more myeloid lines in a pre-treatment specimen

· May occur de novo or following MDS or MDS/MPD

· Mainly in elderly and rare in children

· Often severe pancytopenia

· Dysgranulopoiesis, dyserythropoiesis, dysmegakaryopoiesis

· Blasts positive for CD34 and pan-myeloid markers (CD13 and CD33)

· Frequently: aberrant expression of CD56 and CD7

· Increased incidence of multidrug resistance glycoprotein: MDR-1

· Genetics : similar to MDS

o Often: -7/del(7q), -5/del(5q), +8, +9, +11, del(11q), del(12p), -18, +19,
del(20q), +21

o Less often: t(2;11), t(1;7), 3q21 and 3q26

o t(3;21)(q21;q26): usually therapy related, or associated with CML as a 2^nd
event at blastic crisis

o t(3;5)(q25;q34) is associated with mutilineage dysplasia but no thrombocytosis

· Prognosis: multilineage dysplasia has adverse effect on remission

Therapy-Related AML/MDS

· After cytotoxic chemotherapy and/or radiation therapy

· Two types

o Alkylating agent and radiation therapy related

o Topoisomerase II inhibitor related

Alkylating Agent/Radiation Therapy Related AML/MDS

· Occur 5-6 years after initiation of treatment

· Range: 10-192 months

· Risk related to age and cumulative dosage

· Mutagenic effects of ionizing radiation and alkylating agents

· Two-thirds of cases present as MDS

· One-third of cases present as overt AML with MDS features

· All myeloid cell lines affected

· Dyserythropoiesis

· Ringed sideroblasts in 60% of cases (one-third in excess of 15% of erythroids)

· Hypogranulation and nuclear hypolobation in granulocytes

· Dysplastic megakaryocytes, increased in 25% of cases

· Basophils increased in 25% of cases

· Auer rods in a minority of cases

· Bone marrow biopsy: hypercellular in 50%, normocellular in 25%, hypocellular in 25%, fibrosis in 15%

· Types of AML: M2, M4, M5, M6, M7

· Immunophenotype

o Blasts often CD34+, CD33+, CD13+, frequent aberrant expression of CD56+ and CD7+

o Increased incidence of MDR-1 expression in blasts

· Genetics

o Increased cytogenetic abnormalities

o Similar to de novo MDS, RCMD, RAEB

o Unbalanced translocations

o Deletions of chromosomes 5 and 7 (long arms)

o Chromosomes 1, 4, 12, 14, 18

o Complex chromosomal abnormalities

· Prognosis: Poor response to therapy, poor survival

Topoisomerase II Inhibitor Related AML/MDS

· Epipodophyllotoxins and related compounds that target DNA-Topoisomerase II, examples etoposide and teniposide, also anthracyclines, such as doxorubicin and 4-epi-doxorubicin

· All ages

· Shorter latency: 12-130 months (median: 33-34 months)

· Latency can be less than 6 months

· Usually presents as overt AML without a previous MDS phase

· Significant monocytic component

· Most are acute monoblastic or myelomonocytic, occasionally acute promyelocytic leukemia or acute megakaryoblastic leukemia

· Bone marrow usually hypercellular

· Acute lymphoblastic leukemia also possible, usually associated with t(4;11)(q21;q23) chromosome abnormality

· Genetics:

o Usually balanced translocation involving 11q23 (MLL gene) and primarily t(9;11), t(11;19), and t(6;11)

o Others t(8;21), t(3;21), inv(16), t(8;16), and t(6;9)

o t(4;11)(q21;q23) (associated with ALL)

o t(15;17)(q22;p21) (APL)

· Prognosis: good initial response to therapy, but relapses frequent and survival variable (especially poor with 11q23)

AML not otherwise categorized

· Cases that do not fulfill criteria for inclusion in:

o AML with recurrent genetic abnormalities

o AML with multilineage dysplasia

o AML and MDS, therapy-related

· Basis for subclassification in this category

o Morphology

o Cytochemistry

o Degree of maturation

§ Defining criterion for AML is ³20% myeloblasts in PB or BM (differential for 500 cells in BM, or 200 leukocytes in PB). PB smear and BM aspirate provide the major criteria required for categorization. BM biopsy is for assessment of marrow cellularity in pre- and post-therapy, also for diagnosis of hypocellular acute leukemia cases and leukemia associated with fibrosis

§ Blast equivalents

· Promyelocytes in APL

· Promonocytes in AML with monocytic differentiation

o Megakaryoblasts

· Recommendations for classification are applicable only to specimens obtained prior to chemotherapy.

· Subtypes

o Acute myeloblastic leukemia, minimally differentiated (M0)

o Acute myeloblastic leukemia without maturation (M1)

o Acute myeloblastic leukemia with maturation (M2)

o Acute myelomonocytic leukemia (M4)

o Acute monoblastic leukemia (M5a) and Acute monocytic leukemia (M5b)

o Acute erythroid leukemia (M6)

o Acute megakaryoblastic leukemia (M7)

o Acute basophilic leukemia

o Acute panmyelosis with myelofibrosis

o Myeloid sarcoma

Acute myeloblastic leukemia, minimally differentiated (M0)

· Definition

o Acute leukemia with no evidence of myeloid differentiation by

§ Morphology, and Light microscopic cytochemistry

o Myeloid nature of blasts demonstrated by

§ Immunologic markers, and/or

§ Ultrastructural studies

o Immunophenotyping studies essential to rule out ALL

· Epidemiology

o 5% of cases of AML

o Mostly adults

· Clinical

o Present with marrow failure: anemia, neutropenia, thrombocytopenia

o May have leukocytosis with increased blasts

· Blasts

o Medium size

o Round or slightly indented nuclei

o Dispersed nuclear chromatin

o 1 or 2 nucleoli

o Agranular cytoplasm

o Myeloperoxidase (MPO): negative

o Sudan Black B (SBB): negative

o Naphthol ASD chloroacetate esterase: negative

o Alpha naphthyl butyrate esterase: negative or weak reactivity

· BM: markedly hypercellular with poorly differentiated blasts

· Ultrastructural studies: may demonstrate MPO activity

· Blast immunophenotype: positive for

o One or more pan-myeloid antigen

§ CD13, CD33, CD117 (all cases)

o Primitive hematopoietic associated antigens

§ CD34, CD38 and HLA-DR (most cases)

o TdT (1/3 of cases or more)

o Antigens associated with, but not specific for, lymphoid differentiation

§ CD7, CD2, CD19 (frequently)

· Blast immunophenotype: negative for

o B and T lymphoid restricted antibodies

§ cCD3, cC79a, and cCD22

o MPO often negative (may be positive in a few blasts)

o Antigens associated with myelomonocytic maturation

§ CD11b, CD15, CD14, CD65

· Genetics

o No unique abnormality

o Most common: complex karyotypes, +13, +8, +4, -7

· Prognosis is poor: lower remission rate, more frequent early relapse, shorter survival

Acute myeloblastic leukemia without maturation (M1)

· Definition

o Characterized by a high percentage of BM blasts without significant evidence of maturation to more mature neutrophils

o Blasts ³90% of non-erythroid cells

o The myeloid nature of blasts is demonstrated by: MPO or SBB positivity (>3%) and/or Auer rods

· Epidemiology

o 10% of cases of AML

o Adults (median age 46 y/o), but can occur at any age

· Clinical

o Present with marrow failure: anemia, neutropenia, thrombocytopenia

o May have leukocytosis with markedly increased blasts

· Blasts

o Typical myeloblasts with azurophilic granules, and /or Auer rods

o Lymphoblast-like with no granules

· MPO and SBB variably positive (but always positive in ³3% of blasts)

· BM

o Usually markedly hypercellular

o Blasts in BM sections may react with antibodies to MPO, Lysozyme, CD117, and/or CD34

· Differential diagnosis

o ALL, if

§ Blasts have no granules

§ Low percentage of MPO positivity

§ Resolution: TdT, MPO, SBB

o AML with maturation (M2), with a high percentage of blasts

§ Resolution: % promyelocytes and more mature neutrophils more than 10% of nucleated cells

o Acute monoblastic leukemia (M5a)

§ Resolution: NSE, MPO, SBB

o Acute megakaryoblastic leukemia (M7)

§ Resolution: CD41, CD61, MPO, SBB

· Blast immunophenotype: positive for

o Two or more myelomonocytic antigens (CD13, CD33, CD117) and/or

o MPO

o CD34

· Blast immunophenotype: negative for

o Markers associated with monocytic maturation

§ CD11b, CD14

o Lymphoid antigens

§ CD3, CD20, CD79a

· Genetics

o No specific chromosomal abnormalities

· Prognosis

o Aggressive course (particularly with hyperleukocytosis)

Acute Myeloblastic Leukemia with Maturation (M2)

· At least 20% blasts in bone marrow or blood (but less than 90%)

· Granulocytic elements (promyelocytes through PMNs) at least 10% of non-erythroid cells

· Monocytic elements <20% of non-erythroid cells

· 30-45% of all AMLs

· All ages, 20% < 25 years, 40% are 60 years or older

· Anemia, thrombocytopenia, neutropenia

· Variable number of blasts in blood

· Bone marrow hypercellular

· Blasts with or without granules

· Auer rods frequent

· Various degrees of dysplasia

· Eosinophils and basophils may be increased

· Differential Diagnoses

o RAEB (if blast numbers are at lower limit)

o AML without maturation (if blast numbers are at upper limit)

o AMML (when monocytes are increased)

· Immunophenotype

o CD13+, CD33+, CD15+

o Often CD34+, CD117+, HLA-DR+

· Genetics

o del(12)(p11-p13) associated with increased basophils

o t(6;9)(p23;q34) (DEK/CAN fusion gene), associated with poor prognosis

o t(8;16)(p11;p13) associated with erythrophagocytosis

· Responds frequently to aggressive therapy

Acute promyelocytic leukemia (M3)

· Definition: AML with t(15;17)(q22;q21);(PML/RARa)

· Variants: hypergranular and microgranular (hypogranular) types

· Epidemiology: 5-8% of AML, age: mid life

· Clinical features:

o Typical (hypergranular) and microgranular APL: DIC

o Microgranular: high WBC with numerous promyelocytes

· Morphology and cytochemistry

o Hypergranular APL: kidney-shaped, bilobed, dense large granules,“Faggot” cells (cells with bundles of Auer rods), MPO: strongly +, NSE: + in 25% of cases

o Microgranular (hypogranular): bilobed, promyelocytes, MPO(strongly)

· BM Bx: hypercellular, cells with abundant cytoplasm and convoluted nuclei

· Immunophenotype:

o CD33, homogenous and bright

o CD13, heterogeneous

o CD34(-)

o CD15(-)

o CD2(+)CD9(+) co-expression

· PML Ab stain: nuclear multigranular vs speckled in normal promyelocytes or
blasts of other AMLs

· Features of APL with variant translocations

o t(11;17)(q23;q21), PLZF on 11

§ No Auer rods, regular nuclei, pseudo Pelger-Huet cells

§ Resistant to ATRA

o t(5;17)(q23;q12), NPM on 5

§ rare, atypical APL, no Auer rods, responds to ATRA

o t(11;17)(q13;q21), NuMA on 11

· Cell of origin: myeloid stem cell to granulocytic lineage

· Prognosis: favorable, use of retinoids in combinatorial protocols with anthracycline-based chemotherapy for front line treatment currently results in long-term survival and potential cure in at least 60% of newly diagnosed patients.

Acute Myelomonocytic Leukemia (M4)

· Blasts at least 20%

· Monocytic cells at least 20% of cells in bone marrow

· Elevated circulating monocytes (usually above 5 x 10⁹/L)

· 15-25% of all AMLs

· Median age: 50 years

· Male-to-female ratio 1.4:1

· Anemia, thrombocytopenia, fever, fatigue

· Morphology:

o Monoblasts – round nuclei, lacy chromatin, one or more prominent nuclei, abundant basophilic cytoplasm, pseudopods, some granules and vacuoles.

o Promonocytes – blast equivalent, more irregular nucleus, more granules

o MPO + (at least 3% of blasts)

o Monocytic elements: non-specific esterase +

o Double staining for MPO and esterase can be present

· Differential Diagnoses

o AML with maturation

o Acute monocytic leukemia

· Immunophenotype

o CD13+, CD33+ (myeloid)

o CD14+, CD4+, CD11b+, CD11c+, CD64+, CD36+, lysozyme+

· Genetics

o Non-specific

o Specific abnormalities are under AML with recurrent genetic abnormalities, such as (inv)16: eosinophils with immature granule (purple-violet in color), obscuring cell morphology

o 11q23

· Frequently responds to aggressive therapy

· Variable survival rates

Acute Monoblastic/Monocytic Leukemia (M5)

· At least 80% of bone marrow cells are monoblasts, promonocytes, and monocytes

· Promonocytes are blast equivalents

· Neutrophil elements <20%

· Acute monoblastic leukemia (M5a)– at least 80% monoblasts

· Acute monocytic leukemia (M5b)– less than 80% monoblasts

· M5a: 5-8% of all AMLs, usually young individuals (but may occur at any age), in infancy often with 11q23, extramedullary lesions possible

· M5b: 3-6% of all AMLs, adults with median age of 49 ,years, male-to-female ratio 1.8:1

· Clinical features: bleeding disorders most common presentation, cutaneous and gingival infiltration, CNS involvement, extramedullary masses

· Non-specific esterase activity strongly positive (but weak or even negative in 20%)

· MPO negative (promonocytes may have some positivity)

· DDx for Acute Monoblastic Leukemia

o AML, minimally differentiated

o AML, without maturation

o Acute megakaryoblastic leukemia

o Soft tissue sarcomas

o Lymphomas

· DDx for Acute Monocytic Leukemia

o AMML

o Microgranular variant of acute promyelocytic leukemia (MPO strongly +)

· Immunophenotype

o CD13+, CD33+, CD117+,

o CD14+, CD4+, CD11b+, CD11c+, CD64+, CD68+, CD36+, lysozyme+

o CD34 usually negative

· Genetics

o Abnormalities of 11q23 with acute monoblastic leukemia (included in AML with recurrent genetic abnormalities)

o t(8;16)(p11;p13) associated with acute monocytic leukemia, erythrophagocytosis by leukemic cells

· Prognosis: both acute monoblastic and monocytic leukemia follow aggressive course

Acute Erythroid Leukemias (M6)

· Definition: acute leukemias characterized by predominant erythroid population

· Two subtypes based on presence or absence of a significant myeloid component

· Erythroleukemia (erythroid/myeloid)

o >50% erythroid precursors of nucleated cells in BM

o >20% myeloblasts of non-erythroid cells in BM

· Pure erythroid leukemia

o >80% immature erythroid of nucleated cells in BM

o No significant myeloblastic component

· Epidemiology

o Adults

o 5-6% of AML

o Pure erythroid leukemia: rare, at any age

o Some CML can undergo erythroblastic transformation

· Clinical features

o Profound anemia

· Normoblastemia

· May evolve from MDS, either RAEB or RA-MLD with or without RS

· Morphology

o BM

§ Hypercellular

§ Megakaryocytic dysplasia

o Erythroid

§ All stages present

§ Frequent dysplasia: megaloblastoid nuclei, multinucleated forms, cytoplasmic vacuoles

o Myeloid: blasts similar to those in AML M1 or M2

· Erythroleukemia (erythroid/myeloid)

o Iron stain: ringed sideroblasts

o PAS: globular or diffuse cytoplasmic staining

o MPO and SBB: may be positive for myeloblasts

· Pure Erythroid leukemia

o Morphology: medium to large-sized erythroblasts with round nuclei, fine chromatin and one or more nucleoli, deeply basophilic cytoplasm, and often vacuolated

o Cytochemistry:

§ PAS positive vacuoles

§ MPO negative

§ Alpha-naphthyl acetate esterase and acid phosphatase positive

· Differential diagnosis of erythroleukemia (erythroid/myeloid)

o RAEB

o AML with maturation and increased erythroid precursors

o AML with multilineage dysplasia

· Differential diagnosis of pure erythroid leukemia

o Megaloblastic anemia due to vitamin B12 or folate deficiency

§ Response to vitamins

§ Less dysplasia

§ Hypersegmented neutrophils

o Other AML; especially megakaryoblastic

§ Concurrent erythroid-megakaryocytic involvement

o ALL, lymphoma

§ Lymphoid markers

· Immunopheotype of erythroleukemia (erythroid/myeloid)

o Erythroid

o MPO negative

o Glycophorin A, hemoglobin A positive

· Myeloblasts

o CD13, CD33, CD117, MPO, +/-CD34, +/- HLA-DR

· Immunophenotype of pure erythroid leukemia

o Glycophorin A and hemoglobin A in more differentiated forms

o Immature forms negative for glycophorin Ap

o Positive for carbonic anhydrase 1, Gero antibody (against the Gerbich blood group)

o CD36 (may also be expressed in monocytes and megakaryocytes)

o Megakaryocytic antigens CD41 and CD61: typically negative or partially expressed

o Negative for MPO, HLA-DR, CD34

· Genetics

o No specific chromosome abnormality

o Complex karyotypes common with chromosomes 5 and 7 frequently affected

· Cell of Origin

o Erythroleukemia (erythroid/myeloid):multipotent stem-cell with wide myeloid
potential

o Pure erythroid leukemia: primitive stem cell with some degree of commitment to the erythroid lineage

· Prognosis and predictive factors

o Erythroleukemia (erythroid/myeloid)

§ Aggressive clinical course

§ May evolve to a prominent myeloblast picture

· Pure erythroid leukemia

o Rapid clinical course

Acute megakaryoblastic leukemia (M7)

· Definition: acute leukemia in which >50% of the blasts are megakaryocytic lineage

· Epidemiology

o Adults and children

o Relatively uncommon, 3-5% of AML

· Clinical features

o Cytopenias, often thrombocytopenia, sometimes thrombocytosis

o Dysplastic features in neutrophils and platelets

o Organomegaly in children with t(1;22) often with prominent abdominal masses

o Bone lytic lesions

· Associated with mediastinal germ cell tumors in young adult males

· Morphology of megakaryoblast: medium to large size, round, slightly irregular nucleus, fine reticular chromatin, one to three nucleoli, basophilic cytoplasm, agranular, bleb or pseudopod formation. Blasts may occasionally be small resembling lymphoblasts

· Morphology/histopathology

o BM

§ Variable: uniform population of poorly differentiated blasts or mixture of poorly differentiated blasts and maturing dysplastic megakaryocytes

§ Variable reticulin fibrosis that may yield a dry tap

o PB: micromegakaryocytes (small cells, one or two round nuclei, condensed chromatin, mature cytoplasm, not to be counted as blasts), megakaryoblastic fragments, dysplastic large platelets, hypogranular neutrophils

· Genetics: not specific except for

o t(1;22)(p13;q13)

§ Infants (less than 1 y/o)

§ Stromal pattern of infiltration mimicking metastatic tumor

· Cytochemistry

o SSB and MPO negative

o PAS and Acid Phosphatase positive, and punctuate NSE

· EM

o Peroxidase activity confined to the nuclear membranes and ER with Platelet Peroxidase (PPO) reaction

· Differential diagnosis

o Minimally differentiated AML

o Acute panmyelosis with myelofibrosis

o ALL

o Pure erythroid leukemia

o Blastic transformation of CML or CIMF

§ History of chronic phase

§ Splenomegaly common

§ Red cell abnormalities in CIMF

§ BCR/ABL in CML

o Metastatic tumors in children

§ Alveolar rhabdomyosarcoma

§ Neuroblastoma

· Immunophenotype

o Platelet glycoproteins

§ CD41, CD61 (cytoplasmic more sensitive)

§ Factor VIII

§ CD42 (mature platelets) less frequent

o Myeloid markers

§ CD13 and CD33 positive

§ MPO, CD34, CD45 and HLA-DR negative

o CD36

o Lymphoid: aberrant CD7

· Genetics

o No unique chromosomal abnormality in adults

o Inv(3)(q21;q26) found in other leukemias

o t(1;22)(p13;q13)

§ Infants (less than 1 y/o)

§ Stromal pattern of infiltration mimicking metastatic tumor

o Young men with germ cell tumors i(12p)

· Cell of origin: precursor committed to the megakaryocytic lineage and possibly erythroid lineage

· Prognosis: poor, particularly in infants with t(1;22)

Variant of AML (M7): Acute myeloid leukemia/transient myeloproliferative disorder in Down Syndrome

· Down Syndrome: increased predisposition to acute leukemia, particularly AML (M7)

Acute myeloid leukemia/transient myeloproliferative disorder in Down Syndrome: usually with spontaneous remission

· Clinical features

o Manifests in neonatal period

o Marked leukocytosis, PB blasts usually >30%, often >50%

o May have prominent extramedullary involvement

· Morphology

o Blasts

§ 12-15 υm round to slightly irregular nuclei

§ Moderate amounts of basophilic cytoplasm, cytoplasmic blebs, coarse azurophilic granules

o Promegakayocytes and micromegakaryocytes frequent

o Dyserythropoiesis common

o Dysgranulopoiesis minimal

o Increased basophils

· Cytochemistry

o Blasts

§ MPO, SBB, TdT negative

§ May have scattered, granular PAS positivity

· EM

o Variable number of blasts with platelet peroxidase reactivity

· Genetics

o Trisomy 21

o Additional clonal abnormalities

§ Trisomy 8 most frequent

§ No t(1;22)

o FISH shows cytogenetic abnormalities in megakaryocytic and erythroid precursors

o Molecular studies: clonality by X-chromosome linked polymorphism analysis

· Cell of origin: myeloid precursor cell with potential for megakaryocytic and erythroid differentiation

· Prognosis: remits spontaneously in one to three months, recurrence and 2nd remission or persistent disease may occur

Acute basophilic leukemia

· Definition

o Acute myeloid leukemia with primary differentiation to basophils

o Some may represent blast transformation in undetected CML

· Epidemiology

o < 1% of AML

· Morphology

o Blasts

§ Medium sized with high N/C ratio, oval or bilobed nucleus, dispersed chromatin, one to three prominent nucleoli

§ Moderately basophilic cytoplasm

· Basophilic granules

· Vacuolation

o Mature basophils sparse

o Dyserythropoiesis

· Cytochemistry

o Metachromatic positivity with toluidine blue

o Diffuse pattern with acid phosphatase

o Some with PAS positivity

o No SBB, MPO or NSE by light microscopy

· EM

o Granules with electron-dense particulate substance, characteristic of basophils or mast cells

o Peroxidase activity in nuclear membrane ER and granules

· BM

o Diffuse replacement by blasts

o Increased basophil precursors

o Mast cell differentiation with distinct morphology: oval nucleus, elongated cytoplasm, close to trabeculae, prominent reticulin fibrosis

· Differential diagnosis

o Blast crisis of CML

o AML subtypes with basophilia

§ AML M2 with 12p or t(6;9)

§ Acute eosinophilic leukemia

§ ALL with prominent coarse granules

· Immunophenotype of blasts

o Myeloid markers CD13, CD33

o Early hematopoietic markers CD34 and HLA-DR

o Lymphoid markers: CD9 (usually) and TdT (sometimes)

· Genetics

o No consistent chromosomal abnormality

o 12p or t(6;9) not identified

o A few cases with de-novo Ph chromosome positive acute leukemia t(9;22)(q34;q11)

· Cell of origin: early myeloid cell committed to basophilic lineage

· Prognosis: generally associated with poor prognosis

Acute panmyelosis with myelofibrosis

· Definition: acute panmyeloid proliferation with accompanying fibrosis

· Epidemiology

o Rare form of AML, primarily adults

o Can be de-novo or secondary to Alkylating-agent chemotherapy and/or radiation

· Clinical features

o Constitutional symptoms: weakness, fatigue

o Marked pancytopenia

o Minimal or no splenomegaly

o Rapidly progressive

· Morphology

o PB

§ Marked pancytopenia

§ RBC with little poikilocytosis or anisocytosis, variable macrocytes, rare normoblasts

§ Occasional immature neutrophils including blasts

§ Dysplastic changes in myeloid cells frequent

§ Atypical platelets

o BM

§ Hypercellular, variable degrees of hyperplasia of erythroid granulocytic and megakaryocytic lineages

§ Foci of immature cells, including blasts throughout

§ Foci of late stage erythroid cells prominent

§ Megakaryocytes conspicuous, small and large with dysplastic features including hypolobation

§ Eosinophilic cytoplasm: PAS +, + antibodies to FVIII, and CD61 +

§ Variable reticulin fibrosis (aspiration frequently unsuccessful)

· Differential diagnosis

o Acute megakaryoblastic leukemia

o Other acute leukemia with marrow fibrosis (AML with multilineage dysplasia and fibrosis)

o Metastatic tumor with desmoplasia

o CIMF: immature cells not prominent, megakaryocytic characteristics, splenomegaly

· Immunophenotype

o Phenotypic heterogeneity

o Blasts: myeloid antigens CD13, CD33, CD117 and MPO

o Some proportion of immature cells expressing erythroid or megakaryocytic antigens

· Genetics: complex abnormalities involving chromosomes 5 and/or 7

· Cell of origin: myeloid hematopoietic stem cell (fibroblast proliferation is only epiphenomenon)

· Prognosis: poor response to chemotherapy and short survival

Myeloid sarcoma

· Definition

o Tumor mass of myeloblasts or immature myeloid cells occurring in an extramedullary site or in bone

o May precede or occur concurrently with acute or chronic myeloid leukemias, MPDs or MDSs

o Initial manifestation of relapse in previously treated AML in remission

· Sites of involvement

o Subperiosteal bone of skull, paranasal sinuses, sternum, ribs, vertebrae and pelvis

o Lymph nodes

o Skin

· Clinical features: can be de-novo or concurrently or preceding AML (may precede AML by months to years)

· Differential diagnosis

o Non-Hodgkin lymphomas (lymphoblastic, Burkitt, large-cell lymphomas)

o Small round cell tumors (neuroblastoma, rhabdomyosarcoma, Ewing’s/PNET and medulloblastoma)

o High index of suspicion in undifferentiated tumors to avoid missing myeloid sarcoma

· Immunophenotype

o Myeloblasts: chloracetate esterase, CD13, CD33, CD117, MPO, CD43

o Monoblasts: CD14, CD116, CD11c, lysozyme, CD68, CD43

· If a tumor is CD43+ and CD3-, then MPO, lysozyme, CD61 should be pursued

· Genetics

o Association with AML with maturation and t(8;21)(q22;q22), AMML Eo with inv(16)(p13q22) or t(16;16)(p13q22)

o 11q23 in monoblastic sarcoma

· Cell of origin: primitive myeloid hematopoietic cell

· Prognosis

o Myeloid sarcoma in a setting of MDS or MPD is equivalent to blast transformation

o Myeloid sarcoma does not generally change the prognosis of the underlying leukemia

o Isolated myeloid sarcoma: radiotherapy may result in very prolonged survival

Acute Leukemias of Ambiguous Lineage

· Definition: acute leukemias in which the morphologic, cytochemical and immuno-phenotypic features of the blasts:

o Lack sufficient evidence to classify as myeloid or lymphoid origin

o Or, have morphologic and/or immunophenotypic characteristics of both myeloid and lymphoid cells

o Or, have both B and T lineages (acute bilineal leukemia and acute biphenotypic leukemia).

· Epidemiology: <4% of all acute leukemias, more frequent in adults

· Etiology: unknown, possible causes: environmental toxins and radiation exposure

· Clinical features

o Related to bone marrow failure: fatigue, infections, bleeding

· Morphology

o Acute undifferentiated leukemia

§ Leukemic cells lack any differentiating features

o Acute biphenotypic and acute bilineal leukemias

§ May present as one subtype of AML

· Monoblastic

· Poorly differentiated myeloid

§ Features of ALL

· Immunophenotype

o Undifferentiated acute leukemia

§ Leukemias lack specific lineage markers

· cCD79a, cCD22, CD3 and MPO

§ Generally don’t express more than one lineage-associated marker

§ Often express HLA-DR, CD34, CD38, may express TdT and CD7

o Bilineal acute leukemia

§ Dual population of blasts, each with distinct lineage: positive for myeloid, lymphoid or B and T-cell markers

§ May evolve into biphenotypic acute leukemia

o Biphenotypic acute leukemia

§ Blasts co-express myeloid and T or B lineage markers

§ Or, concurrent B and T lineage markers

§ Rarely co-express markers for myeloid, T and B lineages

· Biphenotypic acute leukemia

o Co-expression of one or two cross-lineage (non specific) markers is not sufficient for biphenotypic leukemia.

§ Myeloid-antigen positive ALL

§ Lymphoid antigen-positive AML

o Lineage switch after therapeutic intervention

§ Possible expansion of pre-existing minor population of blasts of different lineage following therapeutic suppression of the major population

§ Possible lineage instability

· Criteria for biphenotypic leukemia: score of 2 or more for each of two separate
lineages:

o B-lymphoid:

§ Score 2: cCD79a, cIgM, cCD22

§ Score 1: CD19, CD20, CD10

§ Score 0.5: TdT, CD24

o T-lymphoid:

§ Score 2: CD3, anti-TCR

§ Score 1: CD2, CD5, CD8, CD10

§ Score 0.5: TdT, CD7, CD1a

o Myeloid:

§ Score 2: MPO

§ Score 1: CD117, CD13, CD33, CD65

§ Score 0.5: CD14, CD15, CD64

· Differential diagnosis

o Biphenotypic acute leukemia

§ Myeloid antigen positive ALL

§ Lymphoid antigen positive AML

o Undifferentiated acute leukemia

§ Minimally differentiated AML

§ Unusual precursor-B-cell or T-cell ALL

· Genetics

o High degree of cytogenetic abnormalities

o 1/3 of cases have Ph chromosome, these cases typically have CD10(+) precursor B lymphoid component

o t(4;11)(q21;q23) or 11q23. These cases typically have CD10(–) precursor B lymphoid component with a separate monocytic leukemia component

o T/myeloid biphenotypic or bilineal leukemia do not show cytogenetic findings listed above but have other complex karyotypes

· Molecular Findings: many cases have IgH and TCR rearrangements or deletions

· Cell of origin: multipotent progenitor stem cell

· Prognosis

o Unfavorable, particularly in adults

o t(4;11) or Ph particularly unfavorable

· Therapy: usually aggressive chemotherapy or BMT