Haematological Malignancy 2

week 9

causes of leukaemia

Inherited Predispositions

Infection

Environmental Exposure

Types of inherited predispositions that can cause leukaemia

1. trisomy 21 (down syndrome)

2. fanconi anaemia

(genetic mutation that leads to defective DNA repair pathway)

3. Li-Frameni syndrome

(loss of p53 protein - responsible for detecting DNA damage and cell cycle arrest)

types of infections that can cause leukaemia

1. epstein-barr virus (EBV)

(infects B-cells, silences tumour-suppressor genes, disable apoptotic signals)

2. HTLV-1

(Infects CD4+ T-cells, blocks DNA repair, unregulates proliferative genes)

types of environmental exposure that can cause leukaemia

1. benzene and other aromatic hydrocarbons

2. ionising radiation

types of investigations of haematological malignancy

full blood count (FBC)

blood film

In haematological malignancies what would the FBC show for the following parameters: red cell count, platelets, MCV, white cell count

red cell count is variable - can be reduced with suppression of erythropoiesis or bleeding. or can be raised in clonal erythrocyte proliferations (e.g. polycythaemia vera)

platelets - may be reduced with myelosuppression or pooling in the spleen, raised in thrombocythaemia

MCV - usually normal; may be raised during cytotoxic therapy because of cell-cycle arrest

white cell count - variable, reduced WCC if immature cancer cells crowd out healthy production in the bone marrow, raised in lymphoma, if normal still do not rule out leukaemia

blood morphology in acute myeloid leukaemia peripheral blood film

• thin cytoplasm, very large nucleus (‘scant' cytoplasm)

• undifferentiated blasts

blood morphology in chronic myeloid leukaemia peripheral blood film

• neutrophilic leukocytosis* - underlying genetic defect causes overproduction of neutrophils, no maturation arrest

• increased basophils and eosinophils

• full maturation spectrum present of other white cells (all stages of white cell development)

• immature granulocytes (myeloblasts)

*leukocytosis = elevated WCC

how are white cells investigated

microscopy

nuclear structure & chromatin appearance

abnormal maturation of nucleus or cytoplasm

cytoplasmic granules

inclusion bodies and vacuoles

cell shape

presence of progenitor cells

differential count

• automated analysers provide total WCC

• percentage values for each cell type

• 3-point differentiation (lymphocytes, granulocyte, monocytes)

• 5-point differentiation (separates neutrophils, eosinophils, basophils, monocytes, lymphocytes)

what are auer rods

clumps of granulocytic material. only found in cells of myeloid lineage - the granulocytes to be specific!

while mostly observed in immature granulocytes, they’re not excusive to them. Have been documented in mature granulocytes too

purpose of bone marrow examination

• identify abnormal cells

• assess cellularity

• assess degree of infiltration by leukaemic cells

what samples can be taken for bone marrow examination

lymph nodes for initial diagnosis (fine needle aspiration)

bone marrow aspirate - needle inserted into bone and marrow is pulled into a syringe

bone marrow trephine - larger needle removes a core of marrow for histology - needed in some lymphoid leukaemias

immunophenotyping

a laboratory technique used to identify and classify specific types of cells by detecting antigens on their surface or inside them

monoclonal antibodies used against cell-surface markers (CD antigens) - no single CD antigen is individually specific for malignancy, the OVERALL marker profile is interpreted

for haemopoietic investigation, what samples are used for immunophenotyping

• blood

• EDTA bone marrow

explain the process of immunophenotyping

• cells are fixed to prevent lysis

• treated to allow antibody access

• fluorescent-labelled antibodies are then assessed by flow cytometry

what can immunophenotyping distinguish

• distinguishes monoclonal and polyclonal populations

• determines stage of maturity

• distinguishes B and T cells in lymphoid population

what is CD45

a general white cell marker - assessed first in immunophenotyping to identify white cell population

the isolated population is is then examined for positive or negative populations in other markers

if more than 20% of cells show a reaction, it is considered positive

Healthy blood contains a diverse mix of cells. Leukemia creates a massive clone of identical abnormal cells, showing up as a unnaturally uniform population with the exact same surface markers

which marker is used in immunophenotyping to determine myeloid lineage

CD13, CD33, CD34

CD34 indicates blast cells

cytogenetics

the study of genetic material at the cellular level

• establishes karyotype

• identifies specific abnormalities in chromosome structure

**REQUIRED to classify leukaemia using WHO classifications

first step in classification of haematological malignancy

in acute leukaemia, a malignant condition is characterised by…

uncontrolled proliferation of a clonal cell population

poorly differentiated blast cells accumulate in the bone marrow and possible other tissues

how does 1976 French-American British (FAB) classification of leukaemia differ from the WHO classification

what causes symptoms of acute leukaemia

• bone marrow failure

• invasion of organs

• metabolic disturbances

symptoms of acute lymphoblastic leukaemia