Myeloproliferative neoplasms

Question 1

What are the four main WHO classifications of myeloproliferative neoplasms?

Answer 1

• CML
• Polycythaemia Vera
• Essential thrombocythaemia
• Primary myelofibrosis

Question 2

When does clonal expansion occur in CML?

Answer 2

• During accelerated phase (= blast crisis)

- This clone tends to be lineage specific (usually myeloid, less commonly lymphoid)

Question 3

Production of what cells are affected in CML?

Answer 3

• RBCs
• Platelets
• WBC subsets (basophils, neutrophils, eosinophils and monocytes)

Question 4

What full blood count measure is a good indicator of CML?

Answer 4

• Increased basophil count

Question 5

What is the major cytogenetic abnormality in CML and how can it be detected?

Answer 5

• t(9;22)(q34;q11) leading to BCR-ABL1 gene fusion on der(22) = Philadelphia chr
• chimaeric abnormal protein = enhanced tyrosine kinase activity
• can be detected by karyotype, FISH and PCR

Question 6

What is the main drug that targets CML and what type of drug is it?

Answer 6

• imatinib
• tyrosine kinase inhibitor
• designed to fit into ATP binding site of chimaeric protein - if blocked it is effectively switched off

Question 7

What type of FISH probe is used for detection of BCR-ABL1 gene fusion?

Answer 7

• Dual fusion probe
• Normal interphase pattern is 2R2G
• BCR-ABL1 positive cells = 1R1G2F (2 fusions)

Question 8

What are the three main types of response in CML therapy?

Answer 8

• Haematological response
• Cytogenetic response
• Molecular response

Question 9

What are the sub-criteria for haematological response in CML?

Answer 9

• Normalisation of blood counts

- Disappearance of splenomegaly

Question 10

What are the sub-criteria for cytogenetic response in CML?

Answer 10

• Major cyto response = more than 65% Ph negative

- Complete Cyto response = 100% Ph negative

Question 11

What percentage of newly diagnosed CML patients taking imatinib achieve complete cytogenetic remission?

Answer 11

Three quarters (75%)

Question 12

Do patients with complete cytogenetic remission still harbour leukaemic cells in their bodies?

Answer 12

• Yes but at a very low level

- Patients with low transcript numbers are less likely to relapse

Question 14

Molecular response to treatment in CML is assessed based on size of the log reduction in number of Philadelphia chr positive cells. What are the subcategories?

Answer 14

• Less than major = less than 3 LR
• Major = greater than or equal to 3 LR in two consecutive samples
• Complete = BCR-ABL1 negative in two consecutive samples of adequate sensitivity (greater than or equal to 4 LR)

Question 15

A 3+ log reduction in BCR-ABL is achieved by an estimated how many imatinib patients?

Answer 15

Two thirds (66%)

Question 16

What is the difference between primary and acquired resistance in CML?

Answer 16

• Primary resistance = failure to achieve a response

- Acquired resistance = loss of a confirmed response

Question 17

Provide some details on primary resistance in the context of haematological and cytogenetic response

Answer 17

Primary haematological resistance:

• failure to achieve a complete haematological response in chronic phrase
• failure to return to chronic phase when in advanced disease

Primary cytogenetic resistance:
- failure to achieve a complete/major cytogenetic response

Question 18

What are the most common mechanisms of resistance in CML?

Answer 18

• BCR/ABL mutations

- Kinase domain mutations account for more than 50% of acquired resistance

Question 19

In what scenarios should mutation analysis be performed in CML?

Answer 19

• Primary treatment failure
• Loss of haematological/cytogenetic response
• Sub-optimal response
• Transcript level increase more than 1 log on 2 occasions
• Before switching to a second line tyrosine kinase inhibitor

Question 20

If a BCR-ABL mutation is identified what happens?

Answer 20

A specific tyrosine kinase inhibitor will be given dependent on the mutation involved

Question 21

What is polycythaemia Vera?

Answer 21

Expansion of the erythrocyte lineage characterised by high peripheral red blood cell count numbers

Question 22

What is essential thrombocythaemia?

Answer 22

Sustained increase in platelets with associated effects

Question 23

What is primary myelofibrosis?

Answer 23

Clonal disorder caused by transformation of early haematopoietic progenitor cells resulting in bone marrow fibrosis

Question 24

Mutations in three main genes are involved in polycythaemia Vera, essential thrombocytopenia and primary myelofibrosis. What are they?

Answer 24

• JAK2
• CALR
• MPL

Question 25

Provide details on MPL mutations in myeloproliferative neoplasms

Answer 25

• MPL encodes thrombopoietin receptor
• Mutations found in 3-10% of patients with essential thrombocytopenia or myelofibrosis
• Most common mutation hotspot is W515

Question 26

Provide some details on JAK2 mutations in myeloproliferative neoplasms

Answer 26

• JAK2 is a tyrosine kinase downstream of many receptors including that of EPO
• JAK2 mutations found in 97% of patients with PCV and 50-60 of those with essential thrombocytopenia and primary myelofibrosis
• Common mutation is V617F (mutations may also occur in exon 12)

Question 26

Provide details on CALR mutations in myeloproliferative neoplasms

Answer 26

• CALR mutations affect 1/3 of patients with essential thrombocytopenia or myelofibrosis
• Mainly Frameshift mutations
• Most common are a 5bp insertion (50%) or a 52bp deletion