Blood And Lymph- Fischler

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Blood and Lymph- Fischler

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Blood and Lymph- Fischler

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Potential causes of erroneous increase in white blood cell (WBC) with automated cell counters:

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-Unlysed red cells, nucleated red cells
-Platelet clumping
-Monoclonal proteins, cryofibrinogen, cryoglobulin
-Heparin

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Potential causes of erroneous decrease in WBC with automated cell counters:

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-Smudge cells
-Clotting
-Uremia plus immunosuppressants

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Mechanisms and Causes of Leukocytosis

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Increased production in the marrow
-Inflammation, chronic infection, Paraneoplastic,
-Myeloproliferative disorders
Increased release from marrow stores
-Endotoxemia, infection, hypoxia
Decreased margination
-Exercise, catecholamines
Decreased extravasation into tissues
-glucocorticoids

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What is the most common cause of neutropenia (agranulocytosis)?

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drug toxicity.

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Name the three chronic nonspecific lymphadenitises

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1. Follicular hyperplasia:
-activation of humoral immune responses.
-ex: rheumatoid arthritis, toxoplasmosis, early stages of HIV infection

2. Paracortical lymphoid hyperplasia:
-stimulation of the T-cell mediated immune response
-ex: infectious mononucleosis, acute viral infections

3. Sinus Histiocytosis (reticular hyperplasia)
-increase in the number and size of cells that line the lymphatic sinusoids
-ex: in lymph nodes draining cancers

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Antigen Designations:

CD 45 is present where?

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on all leukocytes (LCA) leukocyte common antigen

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Antigen Designations:

CD1, CD3, CD4, CD5, CD8 are primarily associated with what?

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Primarilyl T-cell associated

(the lower numbers are T cell... T toddlers)

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Antigen Designations:

CD10 (CALLA), CD19, CD 20, CD 21, CD 23, CD 79a are primarily associated with what?

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Primarily associated B-cell associated

(B is for Big Boys)

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Antigen Designations:

CD 34 is primarily associated with what?

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primarily stem cell and progenitor cell associated.

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Acute Lymphoblastic Leukemia / Lymphoma (ALL). What are these neoplasms consisting of?

Who gets them?

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are neoplasms consisting of immature B (pre-B) or T (pre-T) lymphoblasts.

ALL is the most common malignancy of children and adolescents.

Approx. 85% of ALLs are pre-B cell tumors, typically occur as childhood acute leukemias

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Morphology, Immonuphenotype and genetics of ALL?

there is a positive test for what?

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-diffuse infiltrations of small cells, diffuse chromatin, inconspicuous nucleoli, scant cytoplasm

***>95% of cases are positive for TdT (terminal deoxynucleotidyl-transferase)

Approx. 90% of ALL cases have structural or numerical changes in the chromosomes of the leukemic cells (most common hyperploidy>50 chromosomes)

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What is the most common leukemia of adults in the Western World?

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Chronic Lymphocytic Leukemia (CLL) / Small Lymphocytic Lymphoma (SLL):

-Differ only in the degree of peripheral blood lymphocytosis
-In CLL the absolute lymphocyte count is > 4000/mm3

-SLL constitutes only 4% of NHLs

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Morphology of CLL and SLL... what do yous ee?

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proliferation centers (loose aggregates of larger activated lymphocytes)

and smudge cells (fragile lymphocytes, disrupted in the process of making the smear)

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Immunopheotype and genetics of CLL/SLL? These tumor cells are positive in what?

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CLL and SLL tumor cells are CD19, CD20, and CD5 positive.
-expression of B and T cell markers is abnormal.

Chromosomal translocations are rare in CLL/SLL.

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What can CLL and SLL transform into?

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Prolymphocytic transformation:
-Most common
-15% to 30% of patients. Prolymphocytes are identified in the peripheral blood. Patients have worsening cytopenias, increasing splenomegaly.

Richter syndrome:
-Is a transformation to diffuse large B-cell lymphoma, occurs in
-5%-10% of patients
With both transformations: survival < 1 year

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What is the most common form of indolent Non-Hodgkin Lymphoma in the US?

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Follicular Lymphoma.

-Presents in middle age, males = females
-Arises from germinal center B cells

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Immunophenotype and genetics of follicular lymphoma...

where is there a translocation? what does that lead to an overexpression of?

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-CD19 CD20 CD10 positive

-CD5 negative

-***t(14;18), 90% of cases, leads to overexpression of BCL2
-[ a (14;18) translocation juxtaposes the IgH locus on chromosome 14 and the BCL2 locus on chromosome 18]

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What is the most common form of Non-Hodgkin lymphoma?

What age does this occur in?

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Diffuse Large B-cell Lymphoma:

-25,000 new cases each year in the US
-slight male predominance
-median age about 60 yrs

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What are the special subtypes of Diffuse Large B-cell Lymphoma?

What are the associated viruses for each subtype?

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Immunodeficiency-associated large B-cell lymphoma:
-Occur in the setting of severe T-cell immunodeficiency
-Neoplastic B cells are usually infected with Epstein-Barr virus

Primary effusion lymphoma:
-Most occur in patients with advanced HIV infection or in the elderly
-Tumor cells are infected with KSHV/ HHV8

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Burkitt's Lymphoma... what translocation is this associated with?

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-Tumor of mature B cells

-***Associated with translocations of the c-MYC gene on chromosome 8; usually IgH locus [t(8;14)], but also Ig k [t(2;8)] or delta [t(8;22)] light chain loci.

-endemic tumors are latently infected with EBV

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Morphology of Mantle Cell Lymphoma

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-Tumor cells resemble normal mantle zone B cells that surround germinal centers

-Frequent sites of extranodal involvement: bone marrow, splenic white pulp zones, hepatic periportal areas, gut

-***Multifocal small bowel and colon mucosal involvement produces lymphomatoid polyposis.

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Immunophenotype and genetics of mantle cell lymphoma... what is expressed in high levels?

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-Tumor cells: CD19, CD20 positive

-Usually CD5 positive

-CD23 negative

-***Express high levels of cyclin D1
(11;14) translocation involves the IgH locus on chromosome 14 and the cyclin D1 locus on chromosome 11, leads to overexpression of cyclin D1

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In Marginal Zone Lymphoma, extranodal tumors are referred to as what? What is the origin of these tumor cels?

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-Is a heterogeneous group of B-cell tumors
Arise within lymph nodes, spleen, or extranodal tissues.

-Extranodal tumors: Are referred to as tumors of mucosa - associated lymphoid tumors (MALToma)

-Tumor cells : memory B-cell origin

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What are three main features of marginal zone lymphomas occurring at extranodal sites?

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Develop in tissues involved by chronic inflammatory disorders of autoimmune (example: Sjogren disease and Hashimoto thyroiditis) or Infectious origin (example: Helicobacter gastritis)

Remain localized for prolonged periods
Spread systemically late in their course

May regress if the inciting agent is eradicated

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Who gets Hairy Cell Leukemia?

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A rare B-cell neoplasm

Constitutes approx. 2% of all leukemias

Occurs in middle-aged white men ; Median age: 55 years

Male > Female (5:1)

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What do the cells look like in Hairy cell?

What happens if the bone marrow is involved?

What is contained within the cell?

What do you clinically see?

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Leukemic cells have round, oblong or reniform nuclei/ pale blue cytoplasm / fine hairlike cytoplasmic projections

Bone marrow involved (presence of reticulin fibrils can cause “dry tap”)

Cells contain tartrate resistant acid phosphatase - TRAP (diagnostic stain)

on physical exam there is an enlarged spleen, and sometimes this is the only abnormality that you get.

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Which CD do you see most in the work up of Hairy cell?

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CD11c...

also...
CD19 and CD20 positive
Express surface Ig (usually IgG)
Express the monocyte-associated antigen CD11c, CD25, and CD103

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What is the 'wastebasket' diagnostic category?

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Peripheral T-cell lymphoma, unspecified.

-Tumors with a mature T-cell phenotype

-Consist of a pleomorphic mixture of small, intermediate, and large-sized malignant T cells

-Usually with generalized lymphadenopathy, may be accompanied by pruritus, fever, eosinophilia and weight loss

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What rearrangements of what gene do you see in Anaplastic Large Cell Lymphoma?

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rearrangements of ALK gene on chromosome 2p23.

morphology: large anaplastic cells, horse shoe shaped nucleai, voluminous cytoplasm (hallmark cells)

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In Adult T-cell Leukemia/Lymphoma, which T-cells has the neoplasm? what infection is associated with this? What do the cells look like?

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A neoplasm of CD4 + T cells

**Associated with HTLV - 1 infection (is endemic in Southern Japan and the Caribbean basin, and West Africa)

Characterized by generalized lymphadenopathy, hepatosplenomegaly, peripheral blood lymphocytosis, hypercalcemia and skin lesions

**Cells frequently appear with multilobated nuclei (flower or cloverleaf cells)

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In what disease do you see generalized puritic erythematous rash (no hypercalcemia), and is a tumor of the CD4+ helper T cells?

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Mycosis Fungoides / Sézary Syndrome

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What's the name of the microabscesses that you see in the epidermis? What are the 3 distinct cutaneous stages?

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3 distinct cutaneous stages:
-Premycotic phase
-Plaque phase
-Tumor phase

Neoplastic T-cells infiltrate epidermis and upper dermis
With progression spreads to lymph nodes and bone marrow

Micro reveals atypical PAS-postive lymphs in epidermis; aggregates of these cells are called Pautier microabscesses.

In Sezary Syndrome, skin involvement is a generalized exfoliative skin rash.

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If you present with a destructive midline mass affecting the nasopharynx, skin and testis, what are you thinkin' about?

What virus is this associated with?

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Extranodal NK/T-cell Lymphoma.
-tumor invades small vessels, leads to extensive ischemic necrosis.

-highly associated with EBV

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What are the two types of Large Granular Lymphocytic Leukemias?

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Cytotoxic T-cell disease:
-mild to moderate lymphocytosis and splenomegaly

NK-cell Disease:
-little or no lymphocytosis

morphology: large lymphocytes with abundant blue cytoplasm containing corase azurophilic granules.
clinical: neutropenia, anemia ass'd with pure red cell aplasia, increased incidence of rheumatic disorders.

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in Plasma Cell Myeloma (multiple myeloma), where does these neoplastic plasma cells produce multiple tumors?

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in the skeletal system. multiple myeloma is the most common primary tumor arising in BONE of adults.

Bone marrow: usually greater than 30% plasma cells.

BONE pain is the most common symptom.

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What type of cells are you going to see in multiple myeloma?

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Neoplastic plasma cells/morphologically abnormal plasma cells (myeloma cells)
Bone marrow: usually greater than 30% plasma cells
Plasmablasts
Bizarre multinucleated cells
Flame cells
Mott cells
Russell bodies (cytoplasmic)
Dutcher bodies (nuclear)

Blood:
normochromic normocytic anemia
leukocyte count: may be normal, slightly decreased, or slightly increased
platelet count: may be decreased, or normal
rouleaux formation (due to increase of globulins)

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What is the most common serum monoclonal immunoglobulin you is gonna see?

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***IgG.

clinically, you also will see amyloidosis, spike in Bence Jones protein

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In Monoclonal Gammopathy of Uncertain Significance (MGUS), what percentage of people get it at what age? What can this progress into?

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Occurs in approx. 3% of people >50 years of age and in approx. 5% of people > 70 years of age. Patients are asymptomatic and the serum M protein level is < 3 gm/dL

Approx. 1% of patients with MGUS progress to a symptomatic plasma cell dyscrasia (usually multiple myeloma) per year.

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_____ is a B cell neoplasm, that usually secretes monoclonal IgM, often at high enough levels to cause a hyperviscosity syndrome (Waldenström macroglobulinemia)

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Lymphoplasmacytic Lymphoma

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What is the lymphocytic component that is positive in Lymphoplasmacytic Lymphoma? Where is there a chromosome deletion?

When does it present?

Prognosis?

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Lymphocytic component: CD20 positive

Plasma cell component: expresses and secretes immunoglobulin usually IgM

Deletion involving chromosome 6q

Prognosis: incurable, tx is plasmapheresis.

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What is the most common isotype in primary or immunocyte-associated amyloidosis?

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lambda.

characterized by monoclonal plasma cells secreting light chains that are deposited as amyloid.

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Ok, here's an easy one. What is the malignant neoplastic cell in Hodgkin Lymphoma?

What does it look like histologically?

They are positive for which CDs?

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Reed-Sternberg (RS) Cells.. need to see them to make the dx.

Owl-eye appearance (bilobed nucleus with prominent central nucleoli surrounded by clear space)

RS are positive for CD15 and CD30

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Variants of Reed-Sternberg cells

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Mononuclear variants- have a single oblong or round nucleus and large inclusionlike nucleolus

Lacunar cells - have multilobated nuclei and abundant pale cytoplasm. Nucleus appears to be in an empty hole (the lacuna).

Lympho- histiocytic variants (L & H cells) - have polypoid nuclei that look like popcorn kernels (have inconspicuous nucleoli, and moderately abundant cytoplasm)

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What are the four classical forms of Hodgkin's Lymphoma?

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1. Nodular sclerosis - is the most common form of HL (65% to 70% of cases); EBV-
Characterized by: lacunar cells, and collagen (fibrous) bands; background infiltrate

2. Mixed cellularity - accounts for approx. 20%-25% of cases; eosinophils and plasma cells; EBV+; background infiltrate

3.Lymphocyte rich - uncommon; EBV +
-Background infiltrate rich in T lymphocytes

4. Lymphocyte depletion- least common form of HL; <5% of cases; EBV+

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What is the nonclassical variant of HL?

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Lymphocyte predominance –uncommon, accounts for approx. 5% of all cases. has L-H cells (popcorn cell) and are negative for CD15 and CD30; EBV-

Background (reactive B cells and follicular dendritic cells)

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Does Hodgkins Lymphoma have a predictable course? If so, what is it? What does it usually present with?

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The spread of HL is predictable.

Nodal disease → Splenic disease → Hepatic disease → Marrow involvement and extranodal disease

Usually presents with a painless enlargement of lymph nodes

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Clinical Features of Nodular Sclerosis and Mixed Cellularity:

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Nodular Sclerosis:
Seen in adolescents or young adults; males = females
Involves supraclavicular, lower cervical, and mediastinal lymph nodes
Stage 1 or 2 disease most common
Excellent prognosis

Mixed cellularity:
males>females, more likely to be seen in older age, associated with systemic symptoms, and >50% present as stage 3 or 4 disease.
prognosis is very good

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Clinical Features of Lymphocyte-rich and Lymphocyte deletion:

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Lymphocyte-rich:
-males > females; older adults
-very good to excellent prognosis

Lymphocyte depletion:
-In older males, HIV-infected individuals or patients in developing countries
-Advanced stage and systemic symptoms are frequent
-Overall outcome may be less favorable

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Lymphocyte predominance clinical features:

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-Typically seen in young (<35 year old) men
-cervical or axillary lymphadenopathy
-Rare mediastinal or bone marrow involvement
-prognosis is excellent

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___: a tumor of hematopoietic progenitors caused by acquired oncogenic mutations that impede differentiation leading to the accumulation of immature myeloid blasts in the marrow

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Acute Myeloid Leukemia

Incidence: Peak, after 60 years of age

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What increases incidence of Acute Myeloid Leukemias?

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Increased incidence with:
viruses, radiation, cytotoxic chemotherapy, benzene, smoking

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What the name of the intracytoplasmic rods in the myeloblasts?
What to stain with?
Key myeloid antigens?

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they is called Auer rods (abnormal lysosomes in myeloblasts, not in ALL)
-stain with myeloperoxidase or Sudan Black
-CD13, CD33, CD117

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Diagnosis of AML?

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Diagnosis of AML is based on the presence of at least 20% myeloid blasts in the bone marrow

Auer rods
-red-staining, needle-like cytoplasmic granules (peroxidase-positive)
-are derivatives of azurophilic granules

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AML Categories

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AML, minimally differentiated (M0)
AML without maturation (M1)
AML with maturation (M2)
Acute myelomonocytic leukemia (M4)
Acute monoblastic/monocytic (M5)
Erythroleukemia (M6)
Acute megakaryoblastic leukemia

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AML with t(8;21)...who gets it?

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Full range of myelocytic maturation; Auer rods easily found
Cytogenetics: t(8;21)(q22;q22)
Represents 5-12 % of AML
Predominance in young patients
Prognosis: more favorable than AML without recurrent genetic abnormality
Large blasts, abundant basophilic cytoplasm
Frequent Auer rods, dysplasia, abnormal granulation, maturing granulocytes

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-high incidence of disseminated intravascular coagulation (DIC) is found in which AML? What is the M-subtype?

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AML with t(15;17)
-Numerous Auer rods, prominent primary granules (M3 subtype)
-hypogranular or microgranular variant (M3v)
Cytogenetics: t(15;17)(q22;q11-12)PML/RARα

Prognosis: Intermediate

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What do you see in M4 Acute myelomonocytic leukemia?

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M4 Acute myelomonocytic leukemia
monocytic cells 20 – 79 %, granulocytic 30-80 % of nonerythroids
myeloid elements show range of maturation
monoblasts: nonspecific esterase+

Prognosis: variable

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What do you see in AML with inv(16)?

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-Blasts with both neutrophilic and monocytic differentiation,

-Increased eosinophils, immature eosinophils (abnormal basophilic granules)

Cytogenetics: inv(16)(p13;q22)

Prognosis: favorable

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Ok. M5. who do you see this in? What does it present with?

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M5 Acute monoblastic/monocytic leukemia:

seen in OLDER population (those that can afford to drive BMW M5s)
-high incidence of tissue infiltration
-organomegally
-lymphadenopathy

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What do you see in M6? What are the cell surface markers?

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M6 Acute erythroleukemia:

≥ 50 % erythroblasts and ≥ 20 % myeloblasts in nonerythroids
-subtypes M6a and M6b


Cell surface markers:
***Glycophorin A, Hb A in erythroid blasts; CD 13, 33, 117 in myeloblasts

Prognosis: Intermediate

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Acute Megakaryoblastic Leukemia...

what are the markers for detection?

who do you see AML commonly in?

CD61? CD41?

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blasts of megakaryocytic lineage predominate

***markers for detection: GPllb/llla or vWF

associated with marrow fibrosis

***most common AML in Down syndrome

CD61: CPIIb/IIIa glycoproteins on surface
CD41: GPIb

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Myelodysplastic Syndrome (MDS)... why do you have this? What can this lead into?

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A group of clonal stem cell disorders characterized by maturation defects associated with ineffective hematopoiesis and high risk of transformation to acute myeloid leukemia.

peripheral blood cytopenias

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What are the classifications of Myelodysplastic Syndromes (MDS)?

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Classification of MDS includes:
-Refractory anemia
-Refractory anemia with ringed sideroblasts
-Refractory cytopenia with multilineage dysplasia
-Refractory anemia with Excess Blasts (RAEB)
-5q- syndrome

*classification of myelodysplastic syndromes is based on the number of blasts in the marrow.

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What is the sole abnormality in 5q Syndrome?

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5q- Syndrome:

-middle aged – older females
-PB with thrombocytosis, <5% blasts,
-BM with increased hypolobated megakaryocytes, < 5% blasts

Cytogenetics: 5q- is sole abnormality***
Prognosis: Good

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Morphology of MDS

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Morphology:
-there is a disordered or dysplastic differentiation affecting erythroid, granulocytic, monocytic, and megakaryocytic lineages
-ringed sideroblasts (iron in mitochondria)
-megaloblastoid maturation
-nuclear budding abnormalities
-Pseudo-Pelger-Hüet cells (neutrophils with two nuclear lobes)
-pawn ball megakaryocytes

Myeloblasts constitute less than 20% of the overall marrow cellularity

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Myelodysplastic Syndromes Clinical: progression to AML? Who is more likely to have this happen?

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subtypes with a higher proportion of blasts have more severe cytopenias, an increased risk of progression to AML, and a worse prognosis

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What is a common feature in Myeloproliferative Disorders?

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Have increased production of one or more terminally differentiated myeloid elements usually resulting in elevated peripheral blood counts

Common feature: the presence of mutated tyrosine kinases. These circumvent normal controls and lead to a growth factor-independent proliferation and survival of marrow progenitors.
- increased proliferative drive
- extramedullary hematopoiesis
- variable transformation to a spent phase (marrow fibrosis and peripheral blood cytopenias)
- variable transformation to acute leukemia

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Chronic Myeloid Leukemia: What is the tyrosine kinase mutation in this?

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***BCR-ABL fusion gene (100% frequency): derived from BCR gene on chromosome 22 and the ABL gene on chromosome 9, reciprocal (9;22)(q34;q11) translocation (Philadelphia chromosome [Ph])

Slow progression; Median survival, approx. 3 years
Accelerated phase
Blast crisis
-Myeloid blast crisis (70%)
-Lymphoid blast crisis (30%)

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Polycythemia Vera: What is the tyrosine kinase mutation?

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increased marrow production of red cells, granulocytes, and platelets (panmyelosis)

the increase in red cells (polycythemia) causes most of the clinical symptoms

***tyrosine kinase mutation: JAK2 point mutations ( > 95% frequency)

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In Polycythemia Vera, what are the symptoms due to?

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Clinical Course:
Symptoms are usually related to the increased red cell mass and hematocrit:
-Patients have a ruddy cyanosis, pruritis
-Headaches, dizziness, hypertension, and gastrointestinal symptoms are common
-peptic ulceration
-Hyperuricemia
-Patients have increased risk of major bleeding and thrombotic episodes.

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How do you make the diagnosis of Essential Thrombocytosis?

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-Increased proliferation and production of the megakaryocytic elements

-Patients commonly with platelet counts over 600,000 per mm3

**Is a diagnosis of exclusion; features of other chronic myeloproliferative disorders are absent.

-Is associated with tyrosine kinase mutations: JAK2 point mutations ( 50%-60% frequency) and MPL point mutations (5% - 10% frequency), a receptor tyrosine kinase that is normally activated by thrombopoietin

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Essential Thrombocytosis clinical stuff

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Clinical: usually occurs > 60 year old
-Thrombosis and hemorrhage occur
-erythromelalgia (throbbing/burning hands and feet from occlusion of smaller arterioles)
-Is an indolent disorder; has long asymptomatic periods interrupted with hemorrhagic or thrombotic crises
-Median survival: 12-15 years
-May develop into acute leukemia

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What categorizes Priamry Myelofibrosis?

What is the tyrosine Kinase mutations?

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-Characterized by the development of obliterative marrow fibrosis; there is suppression of bone marrow hematopoiesis, resulting in peripheral blood cytopenias and extensive neoplastic extramedullary hematopoiesis in the liver, spleen and lymph nodes

Tyrosine kinase mutations: JAK2 point mutations (50% to 60% frequency) MPL point mutations (5%-10% frequency)

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What causes the extensive collagen deposition in the marrow by non-neoplastic fibroblasts?

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release of PDGF and TGF-beta (released by megakaryocytes)

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What is the morphology of Primary Myelofibrosis?

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Morphology:

-Osteosclerosis
-Large clustered megakaryocytes
-Leukoerythroblastosis=granulocytic and erythroid precursors in the peripheral blood

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Langerhans Cell Histiocytosis:

What do the tumor cells express?
What do these cells have in the cytoplasm?

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Tumor cells express HLA-DR, S-100, and CD1a

cells contain cytoplasmic Birbeck granules. By EM, Birbeck granules are pentalaminar, tubular, and often have a dilated terminal end (has a tennis racket appearance).

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-usually occurs before two years of age; may affect adults
-characterized by cutaneous lesions over trunk and scalp
-associated with lymphadenopathy, hepatosplenomegaly, pulmonary lesions, and osteolytic bone lesions
-marrow infiltration
-fatal if untreated
-50% of patients survive 5 years with chemotherapy (intensive)

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Langerhans Cell Histiocytosis:
Letterer-Siwe Disease (multifocal multisystem Langerhans cell histiocytosis)

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Difference between unicellular and multifocal Eosinophilic Granulomas

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Eosinophilic Granuloma (Unifocal and Multifocal Unisystem Langerhans Cell Histiocytosis)
-erosive expanding accumulations of Langerhans cells usually in the medullary cavities of bones. Most commonly the ribs, femur, and calvarium are involved
cells: Langerhans cells, histiocytes, eosinophils, lymphocytes, neutrophils, plasma cells
-when unifocal, is an indolent disorder, usually involves the skeletal system. Cured by local excision or irradiation. May heal spontaneously
-when multifocal, usually seen in children. Present with multiple erosive bony masses. In 50% of cases, the posterior pituitary stalk of the hypothalamus is involved and diabetes insipidus results.

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Pulmonary Langerhans cell histiocytosis is seen in who?

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seen in adult smokers
(may regress spontaneously with cessation of smoking)
usually is polyclonal --> reactive hyperplasia

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Spleen ruptures usually how?

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-usually caused by a severe blow or crushing injury
-spontaneous rupture, encountered in infectious mononucleosis, typhoid fever, malaria, lymphoid neoplasms
-rupture usually leads to extensive intraperitoneal hemorrhage

treatment: surgical removal

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how can you classify thymomas?

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Thymomas are tumors of thymic epithelial cells.
Classification:
-Tumors that are cytologically benign and noninvasive
-Tumors that are cytologically benign but invasive or metastatic
-Tumors that are cytologically malignant (thymic carcinoma)

Presentation:
-40% - symptoms from impingement on mediastinal structures
-30% - 45% myasthenia gravis patients
-remainder, discovered incidentally, during cardiothoracic surgery or imaging studies