Acute lymphoblastic leukaemia and MLL translocations

Question 1

ALL

Answer 1

Acute lymphoblastic leukaemia
Malignant (clonal) disease of the bone marrow in which early lymphoid precursors proliferate and replace the normal haematopoietic cells of the marrow

Question 2

ALL epidemiology

Answer 2

Most common childhood cancer
80% of acute leukaemia cases
20% of cases in adults
Peak at age 2-5; age 50

Question 3

Presentation of ALL

Answer 3

Pancytopenia; Fatigue; easy bruising; bleeding; extremity pains due to build up of lymphoblasts in bone marrow

Question 4

Clinical presentations (physical exam) ALL

Answer 4

Pallor
Ecchymoses
Petechiae
LAD
Hepatosplenomegaly

Question 5

Clinical presentations (lab abnormalities) ALL

Answer 5

Anaemia
WBC vary
- 0.1 (20-40%)
- 100k (10-16%)
Usually decreased platelets (pancytopenia)
Increased LD, Uric acid
Chest x-ray; enlarged mediastinum
Lumbar puncture; CSF to investigate CNS involvement (5-10

Question 6

Morphologic diagnosis of ALL

Answer 6

FAB classification
L1 small uniform blasts (Paedicatric ALL)
L2 larger, more variable sized blasts (adult ALL)
L3 uniform cells with basophilic and sometimes vacuolated cytoplasm (mature B cell ALL)

Question 7

Immunophenotyping of B-lineage ALL markers

Answer 7

CD19, CD20, CD22, CD24 and CD79a

75% of ALL cases

Question 8

Immunophenotyping of T-lineage ALL markers

Answer 8

CD1a, CD2, CD3(membrane cytoplasm), CD4, CD5, CD7 and CD8, CD2, CD5 and CD7

Question 9

Treatment of ALL

Answer 9

Systemic chemotherapy
Prophylactic CNS chemotherapy and sometimes CNS radiation
For Phil. + ALL, tyrosine kinase inhibitor
Immunotherapy, targeted therapy, stem cell transplantation, radiation
Palliative care

Question 10

____________ is the favourable number in ALL

Answer 10

Hyperdiploid

Question 11

____________ non-favourable number in ALL

Answer 11

Hypodiploid

Question 12

Favourable translocation in ALL

Answer 12

T(12;21) - tel-AML -1 fusion 20% of ALL cases

Question 13

Unfavourable translocations in ALL

Answer 13

T(1;19) E2A-PBX1
T(9;22) Philadelphia BCR::ABL
MLL (11q23)

Question 14

MLL

Answer 14

Mixed lineage leukaemia
Chromosome 11 q23
Found in various immunophenotypes in AML and ALL
Normally expressed in bone marrow haematopoietic cells

Question 15

MLL is cleaved by ______ to generate what two subunits?

Answer 15

Taspase 1
MLLN and MLLC

Question 16

RNA polymerase II binds promoter but cannot proceed with transcription without _______________________ on the histone core

Answer 16

Specific methylation marks

Question 17

MLL mediates methylation of _______within the promoter region of the genes

Answer 17

H3K4

Question 18

Histone H3 and lysine 4 methylation marks permit transcription initiation and __________ allows for extension

Answer 18

H3K36

Question 19

Major MLL fusion partner genes are:

Answer 19

AF4 - ALL
AF9 - AML
ENC - ACC. And AMC

Question 20

MLL partial tandem duplication

Answer 20

Most commonly results from duplication of exons 5-12 and inserted before exon 11 or 12
Creates a unique in-frame fusion of exon 11/12 upstream of exon 5
Most often found in adult de novo AML with normal cytogenetics trisomy 11

Question 21

De novo clinical pathology of MLL leukaemia

Answer 21

MLL arrangements are found in approximately:
5% of ALL
5-10% of AML
Basically all cases of MLL

Question 22

Therapy related clinical pathology of MLL leukaemia

Answer 22

Therapy related
5-10% of 11q23 cases are found mainly following a treatment anti-topoisomerase II, or an intercalating topoisomerase II inhibitor
Also after alkylating agent treatment and/or radiotherapy - the prior cancer is variable

Question 23

HOX gene expression ___________ as haematopoietic cells differentiate

Answer 23

Decreases

Question 24

HOX genes and MLL

Answer 24

Expression must be terminated too early for normal differentiation to complete
Upregulation of HOX genes is central to MLL fusion leukaemia (precursors are unable to differentiate)

Question 25

Minimal residue disease and targets

Answer 25

Residual tumour cells undetected by conventional procedures
Patients in clinical emission may still harbour 10^10 malignant cells
Chromosomal translocations are ideal targets for MRD monitoring
- detection is relatively simple involving PCR with a single set of primers
- chromosomal aberrations are pathogenically related to the neoplastic process and they represent a stable molecular marker

Question 26

ALL in identical twins

Answer 26

1st hit => mutation in uteri ETV6/RUNX1
2nd hit => secondary mutation ETV6 deletion or gain of RUNX1 => ALL

Mutation occurred in one twin, cellular transmission through the placenta

Question 27

MLL partial tandem duplication

Answer 27

BAD PROGNOSIS
Found in adult de novo AML w/ normal cytogenetics or trisomy II

Question 28

What mediates the binding of MLLN to DNA sequences?

Answer 28

AT-hook motifs mediated binding to AT-rich genomic DNA sequences

Question 29

The transcriptional activation domain recruits what co-activator for transcription in MLL epigenetic regulation

Answer 29

CREB-binding protein

Question 30

Within the N terminal region of the MLL protein the transcriptional repression domain contains what two functional subunits?

Answer 30

RD1 contains DNA methyltrasnferase homology domain
RD2 recruits histone deacetylases HDAC1 and HDAC2

Question 31

What does the C terminal domain of the MLL protein contain?

Answer 31

Histone H3 lysine 4 methyltrasnferase activity

Question 32

Why is MLL a master epigenetic regulator?

Answer 32

RNA polymerase 1 binds promoter but cannot proceed without specific methylation marks on histone core
Histone H3 Lysine 4 methylation marks promote transcription
MLL mediates methylation of H3K4

Question 33

What does an MLL fusion protein consist of?

Answer 33

N-terminus of MLL and C terminus of a fusion partner gene