APML

Question 1

Give background of APML. What is the mutation?

Answer 1

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

Question 2

What is the epidemiology of APML?

Answer 2

Uncommon in children, incidence rises until plateau phase in early adulthood
incidence remains constant until the early 60s then decreases

Question 3

What is the t(15;17)(q24;q21) classed as?

Answer 3

Disease defining mutation - does not need any other additional mutations to cause disease

Question 4

What does the PML-rara fusion gene do?

Answer 4

It arrests cells in the promyelocyte maturation

Question 5

What is associated with APML? What is the outcome?

Answer 5

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)

Question 6

How does APML present?

Answer 6

Thrombocytopaenia

with life threatening DIC

Question 7

How is it treated acutely?

Answer 7

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.

Question 8

What is typically seen in a blood film?

Answer 8

Hypergranular variant - faggot cells

Microgranular variant - cleave cells with very little granulation

Question 9

What is typically seen in the red cell indicies?

Answer 9

Sometime because of DIC everything is low

Question 10

What is typically seen on the bon marrow aspirate?

Answer 10

blast cells with granules and multiple auer rods

Question 11

What is seen on flow cytometry?

Answer 11

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 -

Question 12

What is the problem in APML?

Answer 12

There is a maturation block from promyelocyte to myelocyte

Question 13

What should the cytogenetic analysis show?

Answer 13

t(15;17)(q24;q21)

Question 14

How is FISH used to diagnose?

Answer 14

Can visualise the fusion of PML and Rara gene with different coloured probes

Question 15

What are the 2 forms of APML?

Answer 15

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

Question 16

What are the greatest challenges to good prognosis with APML?

Answer 16

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

Question 17

How does the DIC occur?

Answer 17

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.

Question 18

What is the pathophysiology of disease in APML?

Answer 18

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

Question 19

How does ATRA work?

Answer 19

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

Question 20

How has ATRA improved survival?

Answer 20

Survival now 80% increase vs chemo alone

Question 21

What is done immediately to diagnose APML?

Answer 21

FISH analysis - this is quick

Question 22

How does use of Arsenic Trioxide help? + study

Answer 22

ATO - binds to PML and causes cell degradation and killing

leukaemia 2012