Haem 11 - Acute leukaemia Flashcards
chromosomal translocations and inversions in leukaemia
creation of new fusion genes (AML and ALL)
abnormal regulation of genes (mainly ALL)
Types of chromosomal abnormalities in AML
• Types of abnormalities:
o (1) Duplication (usually trisomy) – AML
Trisomy 8 and Trisomy 21
Dosage effect – (having 3 copies of a proto-oncogene rather than 2 may be the underlying trigger of the leukaemia
o (2) Inversion or translocations (alters the DNA sequence)
Creation of new fusion genes – ALL and AML
• AML
o t (8; 21) - RUNX1+RUNX1T1
o 15% of AML
o Partial block – some mature cells remain
• Core Binding Factor – AML
o Inv (16), t (16; 16) fusion gene
o 12% of AML
o Partial block – some mature ‘eosinophil-type’ cells remain
• APML (Acute Promyelocytic Leukaemia) o t (15; 17) PML-RARA
o (3) Loss and part-deletion – AML Most common = del (5q) or del (7q) • Loss of tumour suppressor gene • One copy of an allele may be insufficient for normal haemopoiesis • Possible loss of DNA repair systems
What causes leukaemogenesis in AML?
• Transcription factor dysregulation + chromosomal abnormalities
Transcription factor dysregulation causes an arrest in differentiation (T2 abnormality)
Transcription factor dysregulation is an important contributor to leukaemogenesis
o Not sufficient on its own to cause leukaemia (you need T1 + T2 mutations)
o More genetic hits required (e.g. chromosomal translocation, loss of genetic material, localised DNA mutations)
Proliferation + survival encouraged
Differentiation blocked
Cells do not die like normal
Describe T1 + T2 abnormalities
o Type 1 Abnormalities promote proliferation and survival
o Type 2 Abnormalities block differentiation
Give 2 examples of how transcription factor dysregulation can occur in AML
- t(8; 21)
* inv(16)
Describe how t(8;21) translocation results in block of differentiation
• t(8; 21)
o RUNX1 gene – chr 21 (encodes CBFa)
o RUNX1T1 gene – chr 8
o CBF - core binding factor
- Normal version – RUNX1/CBFa + CBFb + coactivators –-> turn on the target genes
- Translocation 8;21 fuses RUNX1 with RUNX1T1
o Forms a fusion transcription factor which drives the leukaemia ( RUNX1T1 + RUNX1 + CBFb + co-repressors)
o New TF binds co-repressors rather than co-activators partial differentiation block
o With this particular chromosomal abnormality there is SOME MATURATION, these are not all blast cells
Describe how inv(16) results in block of differentiation
o CBF-beta to MYH11 fusion fusion product cannot bind to the DNA sequence partial arrest in differentiation
o Some maturation to bizarre EOSINOPHIL precursors with giant purple granules
• Preferentially blocks differentiation to eosinophils
What kind of abnormality are mutations affecting CBF (core binding factor)?
Type 2 - block differentiation
What is APML associated with?
DIC
Auer rods
Fine granules
What is the abnormality in APML?
o t (15; 17) PML-RARA fusion gene o Detected using FISH
PML gene – Chr 15
RARA gene – Chr 17
o Causes haemorrhage – exhibits DIC and hyperactive fibrinolysis
o Characterised by an excess of abnormal promyelocytes (with rod shaped inclusions Auer rods) + fine granules
o Slightly later block in maturation than in classic AML
Which cells come from myeloblasts
Neutrophils Eosinophils Basophils Monocytes --> Macrophages https://upload.wikimedia.org/wikipedia/commons/f/f0/Hematopoiesis_simple.svg
Cytochemical staining AML vs ALL
Cytochemical stains
Myeloperoxidase
Sudan black stain
Non-specific esterase strain
AML + ve for all
ALL -ve for all
What is used in immunocytochemistry?
monoclonal antibodies
iBest way to determine lymphoid from myeloid (will show antigens)
Immunophenotyping
Best way to identify mutations
Cytogenetic analysis (done on all patients) FISH (done on some patients) Molecular genetic analysis (done on some patients)
Clinical features of AML
o Bone marrow failure (anaemia, neutropoenia/infection, thrombocytopaenia)
RBCs SoB, pallor, anaemia, fatigue
WCC infections – may be severe + life-threatening – septic shock, renal failure, DIC
• DIC is also caused by APML
Platelets bleeding and bruising (APML haemorrhage as fibrinolysis upregulated)
o Local infiltration
Splenomegaly
Hepatomegaly
Gum infiltration (monocytic leukaemia; i.e. APML)
Skin, CNS or other sites (monocytic leukaemia; i.e. APML, also ALL) – i.e. cranial nerve palsies
Lymphadenopathy (occasionally – more in lymphomas)
o Hyperviscosity if WBC is very high retinal haemorrhages or retinal exudates, cerebral effects
ALL versus AML (if no granules or Auer rods how do you tell?)
Immunophenotyping (immunocytochemistry + immunohistochemistry)
What is aleukaemic leukaemia?
no blasts in the blood but there are blasts in BM – if there are no leukemic cells in the blood you need a BM aspirate
Diagnosis of AML
Blood count and film* Bone marrow morphology* Immunophenotyping Cytogenetic analysis (done on all pt) Molecular studies and FISH (done on some pt)
- With or without cytochemistry
Targeted molecular therapy for
o APML
o Ph +ve (CML, but also rare AML cases)
o Biologics
o APML = All-trans-retinoic acid (ATRA) and A2O3
o Ph +ve (CML, but also rare AML cases) = tyrosine kinase inhibitors e.g. imatinib
o Biologics = anti-CD33 antibody (myeloid) linked to cytotoxic antibody (e.g. gemtuzumab ozogamicin
Clinical features of ALL
Childhood cancer
o Bone marrow failure (anaemia, thrombocytopenia, neutropoenia)
o Local infiltration Lymphadenopathy (± thymic enlargement) Splenomegaly Hepatomegaly Testes, CNS (these are ‘sanctuary sites’ as chemotherapy cannot reach them easily) Kidneys Bone (causing pain)
Prognosis in ALL
o Prognosis is very dependent on cytogenetic/genetic subgroups (particularly for B-lineage)
o GOOD Prognosis: Hyperdiploidy t(12;21) t(1;19) Ph +ve; t(9; 22) – improved prognosis with TK inhibitos
o POOR Prognosis:
t(4;11)
Hypodiploidy
• Leukaemogenic Mechanisms in ALL:
o Proto-oncogene dysregulation Chromosomal translocation • Fusion genes • Wrong gene promoter • Dysregulation by proximity to TCR or immunoglobulin heavy chain loci
o Unknown – hyperdiploidy
diagnosis of ALL
Why does immunophenotype matter?
Why does cytogenetic/molecular genetic category matter?
Why does immunophenotype matter?
AML and ALL are treated very differently
T-lineage (15%) and B-lineage (85%) ALL may be treated differently
Why does cytogenetic/molecular genetic category matter?
Ph-positive need imatinib
Treatment must be tailored to the prognosis
ALL how to manage
- Hyperuricaemia
- Hyperkalaemia
- Hyperphosphatemia
- Extreme leukocytosis
- Hyperuricaemia management (hydration, urine alkalinization, allopurinol, rasburicase)
- Hyperkalaemia management (fluids, diuretics)
- Hyperphosphatemia management (aluminium hydroxide, calcium)
- Extreme leukocytosis management (WBC >200 x 10^9/l) – leukaphresis
ALL chemo duration boys vs girls
• Boys treated for longer because testes are a site of accumulation of lymphoblasts
o Girls = 2 years
o Boys = 3 years
Steps in ALL chemo
remission induction –> consolidation + CNS therapy –> intensification –> maintenance
** Early intrathecal chemotherapy for all – Done in all patients even if initial LP is negative (6-8 treatments)
Leukaemia symptoms in children vs adults
In children – bone pain, limping, pallor, bruising, organomegaly
In adults – pallor, bruising, bleeding, infection, organomegaly
• Acute promyelocytic leukaemia
is a medical emergency
• Sudden-onset bleed = APML (blood count and coagulation screen)
