APML Flashcards
Give background of APML. What is the mutation?
This is AML M3 on the morphological criteria
It is classified with a mutation on t(15;17)(q24;q21) PML-RaRa
no blast count is needed
What is the epidemiology of APML?
Uncommon in children, incidence rises until plateau phase in early adulthood
incidence remains constant until the early 60s then decreases
What is the t(15;17)(q24;q21) classed as?
Disease defining mutation - does not need any other additional mutations to cause disease
What does the PML-rara fusion gene do?
It arrests cells in the promyelocyte maturation
What is associated with APML? What is the outcome?
Severe bleeding, fatal course of only weeks
Chemo only acheives cure in 35% of patients
but new targetted therapy increases to a 5 year event free survival of >95% - arsenic trioxide and all trans-retinoic acid(ATRA)
How does APML present?
Thrombocytopaenia
with life threatening DIC
How is it treated acutely?
APML with DIC is a medical emergency and requires initiation of combination chemo straight away and supportive measures to correct the coagulopathy and counteract particular complications of therapy: these include fresh frozen plasma for factor replacement and cryoprecipitate for fibrinogen.
What is typically seen in a blood film?
Hypergranular variant - faggot cells
Microgranular variant - cleave cells with very little granulation
What is typically seen in the red cell indicies?
Sometime because of DIC everything is low
What is typically seen on the bon marrow aspirate?
blast cells with granules and multiple auer rods
What is seen on flow cytometry?
Increased forward and sideward scatter due to increased cell size and granularity MPO CD13 and CD33 ++ CD117+CD9+ CD34 and HLA-DR +/- CD15 CD16 and CD65 -
What is the problem in APML?
There is a maturation block from promyelocyte to myelocyte
What should the cytogenetic analysis show?
t(15;17)(q24;q21)
How is FISH used to diagnose?
Can visualise the fusion of PML and Rara gene with different coloured probes
What are the 2 forms of APML?
Hypergranular variant - leukopenia and circulating promyelocytes
Intense azurophilic granula and bundles of auer rods (faggot cells), bilobed/kidney shaped nucleus obscure by cytoplasmic granulation
Microgranular variant - granules scarcely visible on light microscopy
What are the greatest challenges to good prognosis with APML?
Patients may be so unwell from coagulopathy that they die of this before the treatment can begin, therefore correction of coagulopathy is vital
Haemorrhage makes up 50% of early death in APML
How does the DIC occur?
The rearranged RARA gene activates tissue factor promotor and increases the TF expression on the cells, this then activtes the intrinsic coagulation cascade to cause a procoagulant state with consumption of clotting factors -> Haemorrhage
Annexin II expression is increased on the surface of leukemic promyelocyes, this binds plasminogens and tpa which increases plasmin formation by factor of 60 -> primary hyperfibrinolysis
The leukaemic cells have an increased capacity to adhere to vascular endothelium and secrete inflammatory cytokines and tnf-alpha which stimulate expression of prothrombotic activity by endothelial cells.
Recent molecular studies in experimental models of human tumors have demonstrated for the first time that oncogene and repressor gene-mediated neoplastic transformation induces activation of blood coagulation.
What is the pathophysiology of disease in APML?
Mutation by 15;17 leads to abnormal fusion of PML-RARa gene. The RARa gene is encoded on the long arm of chr 17, it binds specific response elements (RARE) at the promotor region of target genes. When retanoic acid is absent, the retinoic acid receptor form heterodimers with RXR and Retanoic acid alpha is bound by a corepressor factor preveting recruitment of corepressor complexes causing transcriptional repression. When retinoic acid binds rara complex it changes its conformation and coactivators are recruited, this leads to cell differentiation, terminal differentiation of promyelocytes occurs
In the PMLRara protein there is higher affinity for the corepressors and normal levels of retinoic acid aren’t enough to displace the corepressors leading to a block in differentiation through NCorHDs which enforce DNA methylation
How does ATRA work?
It is a high dose retinoic acid which is sufficient to displace co-repressors and allow co-activator binding so transcription is able to procees
How has ATRA improved survival?
Survival now 80% increase vs chemo alone
What is done immediately to diagnose APML?
FISH analysis - this is quick
How does use of Arsenic Trioxide help? + study
ATO - binds to PML and causes cell degradation and killing
leukaemia 2012
