Introduction to Leukaemia Flashcards
Define Leukemia
Leukaemia = A group of malignant disorders of HSCs, characteristically associated with ↑ WBCs in BM and/or peripheral blood
Major classifications of leukaemia
Lymphoid vs Myeloid
Acute (Undiff) vs Chronic (Diff)
Haematopoiesis site at gestation
Haematopoiesis site in child/adult
Haematopoiesis site at gestation - liver + spleen
Haematopoiesis site in child/adult - bone marrow
What types of progenitor cells are there ?
- Undifferentiated (multipotent) progenitors - You cannot differentiate between myeloid /lymphoid because they do not show the characteristics of mature cells
- Totipotent/unipotent progenitors - These are committed progenitor cells = have already committed to what they will become when they generate mature cells.
What cells does Leukemia affect ?
Lymphocytes
Neutrophils
Eosinophils
Basophils
Monocytes
Platelets
What are formed from haematopoietic stem cells?
What are progenitor cells?
Haematopoietic stem cells differentiate to produce :
-Common myeloid progenitor and -Common lymphoid progenitor
Progenitors:
- Can divide to produce many mature cells (blood cells)
- Cannot divide indefinitely = eventually differentiate and mature
Heterogeneous pool of progenitors
HSCs potency =
Undifferentiated Progenitor cells potency =
Committed Progenitor cells potency =
HSCs = multipotent
Undifferentiated Progenitor cells = multipotent
Committed Progenitor cells = unipotent
What are hematopoietic stem cells (HSCs) and their features?
HSCs = multipotent = can give rise to cells of every blood lineage
- Self-renew - HSCs can divide to produce more stem cells
- Can divide asymmetrically/symmetrically
- Following asymmetric division, HSC forms more differentiated cells with less potency capacity.
- Asymmetric division maintains pool of stem cells.
What type of disease is leukaemia?
How does leukaemia arise?
Leukaemia = a clonal disease - All the malignant cells derive from 1 single mutant stem cell.
First Mutation in a HSC/progenitor = ↑ oncogenic TFs = arrest differentiation + self-renew (cells permanently divide) = pre-leukaemic state HSCs/progenitors. (-First mutation = pre-leukaemia)
-Second mutation = leukaemia (↑ survival + proliferation)
Outline the incidence of leukaemia
Leukaemia is most common in: 75yrs+ male
Describe the presentation of leukaemia
Presentation varies between types of leukaemia
Typically first presents with symptoms of loss of normal blood cell production :
- Abnormal bruising - due to abnormal platelet production
- Repeating abnormal infection (absence of white blood cells = loss of immune function to fight infection, fever)
- Anaemia (↓ production of RBC, ↓ Hb) = fatigue, SOB, paleness, dizzy
BM usually produces RBCs, WBCs, platelets - Not in leukaemia
What causes anaemia in Leukaemia ?
Reduced production of RBC
In the bone marrow, 3 lineages of cells are formed:
WBC, RBC and platelets
But in Leukaemia, no production of these cells.
Fatigue
Loss of Immune power
Fever
Dizziness
How can we diagnose Leukaemia ?
- Peripheral blood blasts tests (PB)
Checks for presence of blasts (immature cells) and cytopenia
>30% blasts = suspected acute leukaemia - Bone marrow biopsy.
Extract BM from pelvic bone and compare results with PB - Lumbar puncture - Determines if the leukaemia has spread to CSF
What are the ways in which we can categorise Leukaemia ?
Molecular and pathophysiological characterisation of leukaemia
- Cytomorphology
- Immunophenotyping
- Next generation sequencing (to identify mutations causing leukaemia)
- Fluorescence in situ (FISH) Hybridisation
- Flow cytometry - detect membrane/intracellular markers
Studying cells to identify the molecular markers that characterise the cells - cell surface markers, cell morphology, identify mutations causing leukaemia etc.
After diagnosing leukaemia
What is the cause of Leukamia ?
Unclear exact cause of leukaemia
Polyaetiological disease = Combination of predisposing factors - genetic, environmental, lifestyle
Leukaemia = Not usually hereditary disease.
Usually caused by somatic genetic alterations = not present in gametes.
Some rare genetic diseases predispose to leukaemia :
Fanconi’s anaemia, Down syndrome
bc involve genes that are involved in leukaemia = trigger leukaemia as a secondary disease
What are the genetic risk factors of developing Leukaemia ?
Gene mutations - activate oncogenes/inactivate tumour suppressors :
-Involving genes common to other malignancies (TP53-Li-Fraumeni syndrome, NF1-Neurofibromatosis = develop leukaemia + other associated disease) or specific to leukaemia
Chromosome aberrations:
- Translocations (BCR-ABL in CML) - 95% of chronic myeloid leukaemia
- Numerical disorders (Down Syndrome trisomy 21) - secondary leukaemia associated w primary disease
Inherited immune system problems:
- Ataxia telangiectasia
- Wiskott-Aldrich syndrome
What are some environmental risk factors of developing leukaemia ?
Radiation exposure :
- Acute radiation accidents
- Atomic bomb survivors
Exposure to chemicals and chemotherapy:
- Cancer chemotherapy with alkylating agents
- Industrial exposure to benzene
Immune system suppression:
-Organ transplant
What are some lifestyle-related risk factors ?
Adult cancers :
- Smoking
- Alcohol
- Excessive sun exposure
- Overweight
What are some possible childhood leukaemia causes ?
- Exposure to electromagnetic fields
- Nuclear power stations
- Infections during early life
- Parents smoking history
- Foetal exposure to hormones
- Mother’s age when child is born
What is the classification of Leukaemia ?
There are 4 types of Leukaemia:
- Acute Lymphoid/Lymphoblastic leukaemia
- Chronic Lymphocytic leukaemia
- Acute Myeloid/Myeloblastic leukaemia
- Chronic Myeloid/Granulocytic leukaemia
depending on affected cell lineage + onset+cause of disease
Outline Acute Leukaemia
Acute = Rapid onset, short but severe course
- Undifferentiated leukaemia - affects undiff. cells
- Characterised by uncontrolled clonal and accumulation↑ of immature white blood cells (-blast)
Blasts = immature cells - Myeloblast/Lymphoblast
Blood film: ↑ blast cells
slide 26
Outline Chronic Leukaemia
Chronic disease = persists over a long time
Chronic leukaemia:
- Differentiated leukaemia - affects differentiated cells (unipotent)
- Characterised by uncontrolled clonal and accumulation↑ of mature white blood cells ( -cyte )
Cytes = mature cells, cells which have differentiated
slide 28
Why is it difficult to differentiate between lymphoblast and myeloblast?
- Bc the blast cells are very immature
What are the main differences b/w Acute and Chronic?
Age, Onset, Duration, WBC count
Age:
- Acute - Children
- Chronic - Middle aged/Elderly
Onset:
- Acute - Sudden
- Chronic - Insidious
Duration:
- Acute - Weeks/Months
- Chronic - Years
WBC counts:
Acute - Variable
Chronic - High
How is acute leukaemia characterised ?
Characterized by a large number of lymphoblasts (ALL)/myeloid blasts (AML) in bone marrow
=Blood - “undifferentiated leukaemia”.
High number of blasts
What causes an increase in blast cells in Acute Leukaemia?
Normally the process is:
Cell proliferation → Blast cell pool → Mature cells → Cell death (Apoptosis /Necrosis )
In acute leukaemia:
Cell proliferation → Blast cell pool → (Maturation arrest)
Some cells die before maturing.
Cell proliferation/Cell death imbalance = ↑ blast cells
slide 35
What are the typical symptoms of acute leukaemia ?
Typical symptoms of acute leukaemia are due to bone marrow suppression:
Thrombocytopenia: purpura (bruising), epistaxia (nose bleed), bleeding from gums
Neutropenia: Recurrent infections, fever
Anaemia: Fatigue, weakness, tiredness, shortness of breath
Might take a bone marrow biopsy to confirm
Describe Acute Lymphoblastic Leukaemia presentation within the population
Prevalence, Origin, Classification, Treatment+Outcome, Remission stats
Prevalence: Childhood
Origin: Cancer of immature lymphoblasts (produce T-cell+B-cell)
Classification: B-cell and T-cell leukaemia
Treatment: Chemotherapy - Long term side effects are rare
Outcome: 5 year event-free survival.
1/10 patients relapse
Remission in 50% after chemotherapy treatment
Adult ALL - poorer prognosis bc disease presents different cell of origin and different oncogene mutations.
Describe Acute Myeloblastic Leukaemia and its presentation within the population
Prevalence, Origin, Classification, Treatment+Outcome, Symptoms
Abnormal production of WBCs - neutrophils, eosinophils, monocytes, basophils
Prevalence: 70 children aged under 16 diagnosed every year = v rare
Origin: Cancer of immature myeloid WBC - myeloblasts
Classification: Based on FAB system (M0-M7)
Treatment: Chemotherapy , monoclonal antibodies (immunotherapy), allogenic bone marrow transplant.
Outcome - 5 year event-free survival (50-60%)
Symptoms: More bleeding in AML
How to distinguish the difference b/w ALL/AML?
Perform cytomorphological studies to identify the type of blast observed in bone marrow biopsy/blood film
ALL/AML = diff. onset but similar symptoms
Chronic leukaemia is characterised by ………..
↑ number of differentiated cells = differentiated leukaemia
Mature cells (WBCs) Affects cells with lower potency
As haematopoiesis process continues and blood cells mature and differentiate, potency reduces (slide10)
Outline Chronic Lymphocytic Leukaemia
Prevalence, Origin, Symptoms, Treatment, Outcome
Prevalence: 3800 new cases every year. Average age = 70
Origin: ↑ numbers of mature(clonal) lymphocytes in bone marrow + peripheral blood
Symptoms: Recurrent infections, Neutropenia , suppresion of normal lymphocyte function, anaemia, thrombocytopenia, lymph node enlargement, hepatosplenomegaly (enlargement of liver + spleen)
Treatment : Regular chemotherapy to ↓ numbers of mature cells
Outcome: 5 year event-free survival of 83%
Outline Chronic Myeloid/Granulocytic leukaemia
Prevalence, Cell characteristic, Symptoms, Diagnosis, Treatment, Outcome
Prevalence: 742 new cases/yr diagnosed in UK. Late onset (85/90yo)
Cell characteristic: ↑ numbers of mature myeloid WBC
Symptoms: Often asymptomatic and discovered through routine blood tests
Diagnosis: high white cell count (neutrophilia) in blood and bone marrow, presence of Philadelphia chromosome
Treatment: targeted therapy - Imatinib
Outcome: 5-year event-free survival is 90%. If progresses, then allogeneic BM transplant
What is the BCR-ABL oncogene ?
BCR-ABL oncogene = oncogene found through translocation within a small chromosome called Philadelphia chromosome. In 95% CML. Balanced translocation b/w chr9/chr22. slide 45 + notes
BCR - Encodes a protein that needs to be continuously active. Has a strong, active promoter which promotes permanent transcription of BCR gene. Cell needs continuous BCR activity.
ABL - Encodes a protein tyrosine kinase whose activity is tightly regulated (auto-inhibition). Proto-oncogene
BCR-ABL protein has constitutive (unregulated) protein kinase activity as the ABL is now under regulation of the BCR promoter.
slides45/ 46
Outline the consequences of unregulated tyrosine kinase activity due to BCR-ABL
- Proliferation of progenitor cells in the absence of growth factors
- Decreased apoptosis
- Decreased adhesion of cells to bone marrow stroma
= together trigger leukaemia
What is detected in 95% of CML?
Philadelphia Chromosome - chr fusion
BCR-ABL oncogene
What are the applications of the BCR-ABL oncogene ?
95% of cases of CML have a detectable Philadelphia chromosome
Detection of minimal residual disease
Therapy: Drugs that specifically inhibit BCR-ABL e.g. Imatinib
Cases negative for BCR-ABL will require different therapy
What is Imatinib ?
(REVISIT)
Imatinib = A small molecule inhibitor that targets specifically ABL-CML treatment
Used to treat CML containing Philadelphia chr. 5% require diff. therapy
Inhibits continuously active TyrKinase activity of fusion protein resulting from translocation.
ABL gene Tyr kinase Requires ATP to work to phosphorylate substrate therefore fusion protein requires ATP to activate.
Imatinib competes w ATP to bind to pocket = ATP cannot bind = fusion protein cannot phosphorylate substrates (tyrosine aa’s of substrate) = oncoprotein cannot activate downstream pathways = treats CML
Remission induced in more patients with greater durability and fewer side effects
Some patients become drug resistant
Abl gene is a tyrosine kinase and contributes ATP.
Competes with ATP therefore the fusion protein wont be able to phosphorylate the substrates.
Philadelphia chromosome translocation gives rise to …………………………..
a novel oncogene - BCR-ABL
3 stem cell types (potency)
- Totipotent - form following fertilisation, zygote, can diff into all body cells
- Pluripotent - embryo, form all cell types but less versatile than totipotent SCs
- Multipotent - diff into cell lineages: haematopoietic SCs, mesenchymal SCs, neural SCs
Main Properties of Stem Cells
- Self-renewal = production of more stem cells
- Proliferation
- Differentiation
Haematopoiesis starts with ……..
Haematopoietic CD34+ stem cell = multipotent stem cell.
34 = number of transmembrane phosphoglycoproteins = important marker for HSCs
Which pathway is important in haematological cancers?
JAK pathway
All blood cells divide into 3 different lineages
Erythrocytes = oxygen-carrying cells, released into blood
Lymphoid lineage = T-lymphocytes, B-lymphocytes, Natural Killer cells. Lymphocytes = derived from common lymphoid progenitors. Adaptive immune system.
Myeloid Lineage = Granulocytes (BEN), Megakaryocytes, Macrophages. Derived from common myeloid progenitors. Innate immune system, blood clotting
Progenitor cells can be of 2 diff. types:
- Undifferentiated Progenitor Cells = Multipotent. Not mature cells. Give rise to 2 diff. groups of blood cells (lineages). Common Myeloid Progenitor, Common Lymphoid Progenitor
- Committed Progenitor Cells = Unipotent. Already committed to what they will become when they generate mature cells. Only give rise to 1 type of blood cell.
see slide 9
Patients undergoing chemotherapy due to ALL are …………..
highly immunocompromised due to the leukaemia + chemotherapy treatment
= require antibiotics for fever (↑ temp)
