CML and myeloproliferative disorders

Question 1

1. What is polycythaemia?

Answer 1

A condition characterised by raised Hb concentration and raised haematocrit

Question 2

2. What are the two main types of polycythaemia?

Answer 2

Relative – caused by a lack of plasma (associated with alcoholism, obesity and diuretics)
True – caused by an excess of erythrocytes

Question 3

3. What is secondary polycythaemia and what can cause it?

Answer 3

Polycythaemia that occurs due to excessive stimulation by EPO (there is no problem with the bone marrow itself)
Appropriate causes: high altitude, hypoxic lung disease, cyanotic heart disease, high affinity haemoglobin
Inappropriate causes: renal disease (cysts, tumours), uterine myoma, other tumours

Question 4

4. How can myeloproliferative neoplasms be broadly categorised?

Answer 4

Philadelphia positive: CML

Philadelphia negative: polycythaemia vera, essential thrombocythaemia, primary myelofibrosis

Question 5

5. What are the two processes that cell undergo as they develop and how are these different in acute and chronic leukaemia?

Answer 5

Two processes: differentiation + proliferation
Chronic leukaemia: differentiation is intact (produces mature cells) + proliferation is excessive and abnormal
Acute leukaemia: differentiation is abnormal (cells have lost the ability to mature) + proliferation is excessive and abnormal

Question 6

6. What are the main types of myeloid malignancy?

Answer 6

Acute myeloid leukaemia (blasts > 20%)
Chronic myeloid leukaemia
Myeloproliferative disorders
Myelodysplastic syndromes (blasts 5-19%)

Question 7

7. Mutations in which genes are commonly associated with the development of myeloproliferative disorders?

Answer 7

Tyrosine kinase

Question 8

8. What is the normal physiological role of tyrosine kinase?

Answer 8

Transmit cell growth signals from cell surface receptors to the nucleus
They are activated by transferring phosphate groups to itself and downstream proteins
They promote cell growth but they do NOT affect maturation

Question 9

9. Name three genes that are associated with myeloproliferative disorders

Answer 9

JAK2 (V617F)
Calreticulin
MPL

Question 10

10. Which conditions is defined by the presence of one of these mutations?

Answer 10

100% of polycythaemia vera has JAK2 V617F mutation

NOTE: it is also found in 60% of primary myelofibrosis and essential thrombocythaemia

Question 11

11. What is the normal physiological role of JAK2? How is this different in polycythaemia vera?

Answer 11

It is a tyrosine kinase that is normally bound to the inactive EPO receptor
When EPO binds to the receptor, the receptor dimerises, autophosphorylates and phosphorylates JAK2 which promotes cell proliferation
Mutated JAK2 is constitutively active in the absence of EPO thereby driving cell replication in the absence of a stimulus

Question 12

12. What is the diagnosis of myeloproliferative disorders based on?

Answer 12

Clinical features (splenomegaly is particularly important)
FBC 
Bone marrow biopsy
EPO level 
Mutation testing

Question 13

13. Outline the typical presentation of polycythaemia vera?

Answer 13

Often incidental
Hyperviscosity: headaches, visual disturbance, stroke, fatigue, dyspnoea, light-headedness
Increased histamine release: aquagenic pruritus, peptic ulceration

Question 14

14. Outline the principles of treatment of polycythaemia vera.

Answer 14

Reduce haematocrit (aim for < 45%) – venesection, cytoreductive therapy (hydroxycarbamide)
Reduce thrombosis risk – control Hct, aspirin, keep platelets < 400 x 109/L

Question 15

15. What is essential thrombocythaemia?

Answer 15

Chronic myeloproliferative disorder mainly involving the megakaryocyte lineage
Characterised by sustained thrombocytosis > 600 x 109/L

Question 16

16. Outline the typical presentation of essential thrombocythaemia.

Answer 16

Incidental finding (50%)
Thrombosis (arterial and venous) – CVA, TIA, DVT, PE, gangrene
Bleeding (mucous membrane and cutaneous)
Headaches, dizziness, visual disturbance
Splenomegaly (modest)
NOTE: ET can cause both thrombosis and bleeding depending on the way in which the abnormal platelet function

Question 17

17. Outline the treatment options for essential thrombocythaemia.

Answer 17

Aspirin
Hydroxycarbamide
Anagrelide (specifically inhibits platelet function but rarely used because of side-effects)
NOTE: hydroxycarbamide is an antimetabolite that suppresses cell turnover)

Question 18

19. What is primary myelofibrosis?

Answer 18

A clonal myeloproliferative disease associated with reactive bone marrow fibrosis
Characterised by extramedullary haemopoiesis
NOTE: other myeloproliferative disorders can transform into myelofibrosis

Question 19

20. Outline the typical presentation of primary myelofibrosis.

Answer 19

Cytopaenias (anaemia, thrombocytopaenia)
Thrombosis 
MASSIVE splenomegaly 
Hepatomegaly 
Hypermetabolic state (FLAWS)

Question 20

21. What might you expect to see in the blood film of a patient with primary myelofibrosis?

Answer 20

Leucoerythroblastic picture
Tear drop poikilocytes
Giant platelets
Circulating megakaryocytes

Question 21

22. What is a characteristic feature seen on bone marrow aspirate in primary myelofibrosis?

Answer 21

Dry tap

Question 22

23. What might you see on histological analysis of a trephine biopsy in primary myelofibrosis?

Answer 22

Increased reticulin and collagen fibrosis
Prominent megakaryocyte hyperplasia and clustering
New bone formation

Question 23

24. Which mutations would you test for in a patient with primary myelofibrosis?

Answer 23

JAK2 and Calreticulin

NOTE: these are not diagnostic

Question 24

25. What are some bad prognostic features in primary myelofibrosis?

Answer 24

Severe anaemia
Thrombocytopaenia
Massive splenomegaly
NOTE: median survival is 3-5 years

Question 25

26. Outline the treatment options for primary myelofibrosis.

Answer 25

Supportive – RBC and platelet transfusions (usually ineffective because of splenomegaly) Hydroxycarbamide (may worsen anaemia) Ruxolitinib – JAK2 inhibitor Allogeneic stem cell transplantation Splenectomy – dangerous operation but may provide symptomatic relief

Question 26

27. What might you expect to see in the FBC of a patient with CML?

Answer 26

Leucocytosis (MASSIVE) | Normal or raised Hb and platelets

Question 27

28. What would you expect to see in abundance in the blood film of a patient with CML?

Answer 27

Neutrophils Basophils Myelocytes (NOT blasts) NOTE: myelocytes are immature myeloid cells that are NOT blasts (analogous to reticulocytes for red blood cells)

Question 28

29. Briefly describe the natural history of CML before targeted treatment became available?

Answer 28

5-6 years stable phase 6-12 months accelerated phase 3-6 months blast crisis

Question 29

30. What is the Philadelphia chromosome?

Answer 29

CML is caused by a translocation between 9;22 producing a derivative chromosome, 22q, which is called the Philadelphia chromosome

Question 30

32. Explain how this fusion gene results in excessive proliferation of myeloid cells.

Answer 30

Abl is a tyrosine kinase that drives cell proliferation but is rarely expressed unless the cells are receiving a stimulus to proliferation Bcr, on the other hand, is a housekeeping gene that is constitutively active The Bcr-Abl fusion gene means that the tyrosine kinase component is constitutively activated thereby driving cell proliferation in the absence of a stimulus

Question 31

33. List some diagnostic techniques used to identify the disease and monitor response to treatment.

Answer 31

FBC and leucocyte count Cytogenetics and detection of Philadelphia chromosome (FISH) RT-PCR to detect and quantify the number of copies of Bcr-Abl fusion transcript NOTE: RT-PCR transcript % is the most sensitive

Question 32

34. What are some issues associated with 1st generation Bcr-Abl tyrosine kinase inhibitors?

Answer 32

Some people fail to achieve a complete cytogenetic response Non-compliance Side-effects (fluid retention, pleural effusion) Loss of major molecular response (due to resistance mutations)

Question 33

35. List some examples of Bcr-Abl tyrosine kinase inhibitors.

Answer 33

1st generation: imatinib 2nd generation: dasatinib, nilotinib 3rd generation: bosutinib

Question 34

36. What are the next steps in treatment if the first-line fails?

Answer 34

1st line fails (no complete cytogenetic response at 1 year or initial response is followed by resistance)  switch to 2nd or 3rd generation 2nd line fails (inadequate response or disease progresses to accelerated or blast phase)  allogeneic stem cell transplantation