HAEM: Acute leukaemia Flashcards
What are the types of leukaemia?
- Acute and chronic
- Lymphoid and myeloid
What are the characteristics of acute leukaemia?
- Rapid onset
- Early death if untreated (weeks or months)
- Immature cells (blasts)
- Bone marrow failure --> anaemia (pallor, fatigue, SoB), neutropoenia (infections), thrombocytopaenia (bleeding)
Where the mutations in leukaemias occur:
- CML occurs at the pluripotent haemopoietic stem cell level because during the chronic phase it is characterised by overproduction of myelocytes, however, when it turns acute, it can then have a lymphoblastic crisis
- I.E. CML —> ALL blast crisis
- AML can also occur at a pluripotent haemopoietic stem cell level meaning that it presents as a myeloid leukaemia but then relapse later on as an acute lymphoid leukaemia
- I.E. AML –> ALL many years later in relapse
- Other AMLs can occur at a multipotent stem cell level or a granulocyte-monocyte precursor level
What type is the top picture?
Myeloid due to granules seen
What is the epidemiology of AML?
- Incidence increases with age (prognosis is worse with increasing age)
- 40% of patients are adults (mainly older adults)
What types of chromosomal abnormalities which can occur in AML?
- Duplication (trisomy)
- Inversion or translocations (alters the DNA sequence)
- Chromosome loss and part-deletion
Describe duplication in AML.
(1) Duplication (trisomy)
Trisomy 8 and Trisomy 21 (gives a predisposition to AML à as seen in TAM in Down’s syndrome)
There is a possible dosage effect associated with these trisomy’s (having 3 copies of a proto-oncogene rather than 2 may be the underlying trigger of the leukaemia)
What type of leukaemia is shown?
- Acute Promyelocytic Leukaemia / APML; t (15; 17) = PML-RARA
Broadly, what are the outcomes of chromosomal inversion of translocation?
- Creation of new fusion genes
- Abnormal regulation of genes
Give some examples of inversion/translocations of chromosomes in AML.
This creates new fusion genes - occurs in ALL and AML
(1)Acute Myeloid Leukaemia / AML; t (8; 21) –> RUNX1+RUNX1T1 ( 15% of AML)
- Partial block – some mature cells remain
(2)Core Binding Factor – AML / CBF-AML; Inv (16), t (16; 16) –> fusion gene (12% of AML)
- Partial block – some mature ‘eosinophil-type’ cells remain
(3)Acute Promyelocytic Leukaemia / APML; t (15; 17) –> PML-RARA (APML)
What are the two most common chromosomal loss/part-deletions in AML? What is the mechanism of leukaemogenesis here?
- MOST COMMON = del (5q) or del (7q)
Leukaemogenesis from…
- Due to loss of tumour suppressor gene
- One copy of an allele may be insufficient for normal haemopoiesis
- Possible loss of DNA repair systems
What are the risk factors for AML?
- Familial or constitutional predisposition (e.g. Down syndrome)
- Irradiation
- Anticancer drugs
- Cigarette smoking
- Unknown
What molecular changes can cause AML?
(a)Many AMLs have aberrations in chromosome count or structure (many patients with the disease have these abnormalities) and may be directly involved in the development of cancer (discussed in previous cards)
(b) Other patients have molecular changes (apparently normal chromosomes):
- Point mutations (associated with AML) à prognostic implications
- Loss of function of tumour suppressor genes
- Partial duplication
- Cryptic deletion (fusion gene forms deletion of tiny bit of DNA and remaining ends joining up)
What is the leukaemogenesis of AML?
Required multiple genetic hits –> _≥_2 interacting molecular defects (synergise to give leukaemic phenotype)
What are type 1 vs type 2 abnormalities involved in leukaemogenesis in AML?
Type 1 Abnormalities = promote proliferation and survival (anti-apoptosis)
- First stage of an acute leukaemia, but cannot drive the acute phenotype by itself
Type 2 Abnormalities = block differentiation (would normally be followed by apoptosis) –> blast accumulation
- Second stage leads to a phenotypic acute leukaemia
- In most AMLs, there is a block in maturation at this point leading to an excess of blast cells
- These cells have an advantage over the normal cells leading to gradual replacement of the normal cells
Why are transcription factors important in differentiation? Give 2 examples of their disruption in AML.
Transcription factors are very important in differentiation as they:
- Bind to DNA
- Alter structure to favour transcription
- Regulate gene expression
Thus, disruption of transcription factor function can result in failure of differentiation – 2 examples:
- (1) t(8; 21)
- (2) inv(16)
What is the role or Core Binding Factors?
- They are dimeric transcription factor
- Master controllers of haemopoiesis
Which chromosomal aberration in AML makes up 15% of all AML?
Translocation 8;21 fuses RUNX1 (encoding CBF-alpha) with RUNX1T1 – 15% of all AML
- Forms a fusion transcription factor which drives the leukaemia
- New TF binds co-repressors rather than co-activators –> partial differentiation block
Which chromosomal aberration in AML makes up 12% of all AML?
Inversion of Chromosome 16 is another mutation that affects CBF-a – 12% of all AML
- Inversion fuses CBF-beta to MYH11 to form a fusion product that cannot bind to the DNA sequence and leads to an arrest in differentiation
- NOTE: in these 2 examples, there is only one chromosome abnormal however, we tend to see a dominant negative effect (when a single abnormal chromosome dominates over the normal one)*
How can APML present acutely?
Sudden DIC could indicate APML
Causes haemorrhage (e.g. sudden onset bruising or bleeding) – exhibits DIC and hyperactive fibrinolysis
This is due to bone marrow failure (?)
What is the mutation in APML?
t (15; 17) –> PML-RARA fusion gene
Where is the block in cell maturation in APML compared to AML?
Slightly later block in maturation than in classic AML
What is a characteristic feature of APML on blood film?
Characterised by an excess of abnormal promyelocytes (Auer rods)
What are the features of the variant form of APML?
NB: There are two morphological variants of APML but the same phenotypic disease and molecular patterns
Variant form = granules still present at resolution below that of a light microscope so can’t see all of them. Variant form is characterised by bilobed nuclei.
AML Summary
Transcription factor dysregulation is an important contributor to leukaemogenesis
- NOT sufficient on its own to cause leukaemia (you need T1 AND T2 mutations)
- More genetic hits required (e.g. chromosomal translocation, loss of genetic material, localised DNA mutations)
- Differentiation blocked
- Cells do not die like normal
- APML leukaemogenesis:
- Type 1 abnormalities –> promote proliferation and survival (i.e. FLT3-ITD)
- Type 2 abnormalities –> block differentiation (i.e. APML = t(15; 17) PML-RARA)
- CBF-AML Leukaemogenesis:
- Type 1: sometimes mutated KIT
- Type 2: mutation affecting function of CBF
What is the best investigation for differentiating lymphoid from myeloid leukaemias?
Immunophenotyping - shows antigens
What is the best investigation for identifying mutations in AML?
Cytogenetic analysis / FISH / molecular genetic analysis
List 3 types of laboratory investigations used in AML diagnosis.
- Cytological features
- Cytochemistry stains (usuallu not used much; sometimes in developing countries)
- Immunophenotyping - looks at cell surface and cytoplasmic antigens
What are the cytological features of AML?
Cytological features via blood count, blood film and BM aspirate
- Fine-speckled granules (i.e. top-right image is AML)
- Auer rods are pathognomonic of myeloid neoplasms
BUT may have aleukaemic leukaemia i.e. no peripheral blood leukaemic cells –> need to do a BM aspirate)
Which cytochemical stains can be used for AML?
- Myeloperoxidase stain (enzyme present in myeloid cells)
- Sudan Black stain
- Non-specific esterase stain
What are the components of immunophenotyping used in AML?
- Flow cytometry (antibodies tagged to fluorescent antibody)
- Immunocytochemistry (monoclonal antibodies added)
- Immunohistochemistry
- Antigen list
Immunocytochemistry and immunohistochemistry differentiate AML from ALL
What are the clinical features of AML in terms of
- bone marrow failure ?
- local infiltration ?
- lyperviscosity ?
Bone marrow failure (anaemia, neutropoenia/infection, thrombocytopaenia)
- RBCs –> SoB, pallor, anaemia
- WCC –> infections
- Platelets à bleeding and bruising (APML –> haemorrhage as fibrinolysis upregulated)
Local infiltration:
- Splenomegaly
- Hepatomegaly
- Gum infiltration (monocytic leukaemia; i.e. APML)
- Skin, CNS or other sites (monocytic leukaemia; i.e. APML) – i.e. cranial nerve palsies
- Lymphadenopathy (occasionally – more in lymphomas)
Hyperviscosity if WBC is v high –> retinal haemorrhages or retinal exudates
Treatment of AML:
- Supportive
- Chemotherapy
- Targeted molecular therapy
- Transplantation
What supportive treatments are used in AML?
- Red cells
- Platelets
- FFP/cryoprecipitate if DIC
- Antibiotics
- Long line
- Allopurinol, fluid and electrolyte balance
What is the goal of chemotherapy in AML?
Goal: damage DNA of leukaemic cells which lack cell cycle checkpoint control
Combination chemotherapy is used:
- Different MOA that work in synergy
- (!) Ensure non-overlapping toxicity
- Cell-cycle specific drugs; 4-5 courses; after 6 months stop, but consider transplantation if poor prognosis
List some targeted molecular therapies available for AML e.g. in APML and Ph +ve cases.
APML = All-trans-retinoic acid (ATRA - not a type of chemotherapy) and A2O3
Ph +ve (CML, but also rare AML cases) = tyrosine kinase inhibitors
Biologics = anti-CD33 antibody linked to cytotoxic antibody (e.g. gemtuzumab). These target products of other mutated genes.
List 4 determinants of prognosis in AML.
- Patient characteristics
- Immunophenotyping
- Genetics
- Cytogenetics
- Morphology
- Response to treatment
What is the epidemiology of ALL?
- Peak incidence in childhood (MOST COMMON childhood malignancy –> 85% of children are cured)
- Prognosis is worse with increasing age
What are the signs and symptoms of ALL in terms of:
- BM failure?
- Local infiltration?
- Bone marrow failure (anaemia, thrombocytopenia, neutropoenia)
- Local infiltration
- Lymphadenopathy (± thymic enlargement)
- Splenomegaly
- Hepatomegaly
- Testes, CNS (these are ‘sanctuary sites’ as chemotherapy cannot reach them easily)
- Bone (causing pain)
What are the ‘sanctuary sites’ in ALL?
Testes and CNS - these are sites which chemotherapy cannot reach easily
What is seen on blood film in ALL?
- anaemia
- neutropoenia
- thrombocytopaenia
- lymphoblasts
Where does B vs T cell ALL originate?
- B-Lineage ALL - starts in the Bone marrow
- T-Lineage ALL - start in the Thymus (which may be enlarged)
What features are best at predicting prognosis in ALL?
Genetic features
Don’t learn in detail:
- GOOD Prognosis:
- Hyperdiploidy
- t(12;21)
- t(1;19)
- TK inhibitors (Ph +ve; t(9; 22)
- POOR Prognosis:
- t(4;11)
- Hypodiploidy
What are the main leukaemogenic mechanisms in ALL?
Proto-oncogene dysregulation –> chromosomal translocation:
- Fusion genes
- Wrong gene promoter
- Dysregulation by proximity to TCR or immunoglobulin heavy chain loci
Unknown – hyperdiploidy
What are the main investigations used in the diagnosis of ALL? Which is diagnostic?
- Clinical suspicion
- Blood count and film
- BM aspirate
- Immunophenotyping* - diagnostic
- Cytogenetic/molecular genetic analysis
- Blood group, LFTs, creatinine, electrolytes, calcium, phosphate, uric acid, coagulation screen
Why is immunophenotyping and cytogenetic/molecular genetic analysis important in ALL diagnosis?
Immunophenotyping (diagnostic) – important because…
- AML and ALL are treated very differently
- Moreover, B-lineage (85%) and T-lineage (15%) are treated very differently
Cytogenetic/molecular genetic analysis – important because…
- Philadelphia chromosome +ve needs imatinib
- Treatment tailored to prognosis (intensify treatment if bad prognosis)
Treatment of ALL:
- Supportive
- Chemotherapy
- Molecular treatment
- Transplantation
What is the supportive management of ALL?
- Blood products
- Antibiotics (broad-spectrum for fever; prophylaxis for PCP infection)
- General medical care
- Central venous catheter
- Hyperuricaemia management
- Hyperkalaemia management
- Sometimes haemodialysis
Breifly describe the basis of chemotherapy used in ALL.
Systemic = 2-3 years of therapy (induction and consolidation):
- Boys treated for longer because testes are a site of accumulation of lymphoblasts
CNS-specific (done in all patients even if initial LP is negative):
- Can also be done by giving high-dose chemotherapy so that it penetrates the BBB
Give 2 examples of molecular treatments used in ALL.
- TKI for Ph +ve cases
- Rituximab (monoclonal antibodies against CD20)
What is the prognosis of ALL?
Children: 5-year disease-free survival of 80%
Adults: 5-year disease-free survival of 30-40%
Why are boys treated longer in ALL?
Boys treated for longer because testes are a site of accumulation of lymphoblasts
