Haem: CML and myeloproliferative disorders Flashcards
What is polycythaemia?
A condition characterised by raised Hb concentration and raised haematocrit.
What are the two main types of polycythaemia?
Relative - caused by a lack of plasma (associated with alcoholism, obesity and diuretics)
True - caused by an excess of erythrocytes
What is secondary polycythaemia and what can cause it?
- 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
How can myeloproliferative neoplasms be broadly categorised?
- Philadelphia positive: CML
- Philadelphia negative: polycythaemia vera, essential thrombocythaemia, primary myelofibrosis
What are the two processes that cell undergo as they develop and how are these different in acute and chronic leukaemia?
- Two processes: differentiatoin + 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
What are the main types of myeloid malignancy?
- Acute myeloid leukaemia (blasts >20%)
- Chronic myeloid leukaemia
- Myeloproliferative disorders
- Myelodysplastic syndromes (blasts 5-19%)
Mutations in which genes are commonly associated with the development of myeloproliferative disorders?
Tyrosine kinase
What is the normal physiological role of tyrosine kinase?
- 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
Name three genes that are associated with myeloproliferative disorders.
- JAK2 (V617F)
- Calreticulin
- MPL
Which conditions is defined by the presence of one of these mutations?
100% of polycythaemia vera has JAK2 V617F mutation
NOTE: it is also found in 60% of primary myelofibrosis and essential thrombocythaemia
What is the normal physiological role of JAK2? How is this different in polycythaemia vera?
- It is a tyrosine kinase that is normally bound to the inactive EPO receptor. When EPO binds to the receptor, the receptor dimersises, autophosphorylates and phosphorylates JA2 which promotes cell proliferation.
- Mutated JAK2 is constitutively active in the absence of EPO thereby driving cell replication in the absence of a stimulus.
What is the diagnosis of myeloproliferative disorders based on?
- Clinical features (splenomegaly is particularly important)
- FBC
- Bone marrow biopsy
- EPO level
- Mutation testing
Outline the typical presentation of polycythaemia vera?
- Often incidental
- Hyperviscosity: headaches, visual disturbance, stroke, fatigue, dyspnoea, light-headedness
- Increased histamine release: aquagenic pruritis, peptic ulceration
Outline the principles of treatment of polycythaemia vera.
- Reduce haematocrit (aim for <45%) - venesection, cytoreductive therapy (hydroxycarbamide)
- Reduce thrombosis risk - control Hct, aspirin, keep platelets < 400x109/L
What is essential thrombocythaemia?
Chronic myeloproliferative disorder mainly involving the megakaryocyte lineage
Characterised by sustained thrombocytosis > 600 x109/L
Outline the typical presentation of essential thrombocythaemia.
- 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
Outline the treatment options for essential thrombocythaemia.
- Aspirin
- Hydroxycarbamide
- Anagrelide (specifically inhibits platelet function but rarely used because of side-effects)
NOTE: hydroxycarbamide is an antimetabolite that suppresses cell turnover
Outline the prognosis for essential thrombocythaemia.
- Normal life span in many patients
- 5% in 10 years risk of leukaemic transformation
- Myelofibrosis is uncommon
What is primary myelofibrosis?
- A clonal myeloproliferative disease associated with reactive bone marrow fibrosis
- Characterised by extramedullary haemopoeisis
- NOTE: other myeloproliferative disorders can transform into myelofibrosis
Outline the typical presentation of primary myelofibrosis.
- Cytopaenias (anaemia, thrombocytopaenia)
- Thrombosis
- MASSIVE splenomegaly
- Hepatomegaly
- Hypermetabolic state (FLAWS)
What might you expect to see in the blood film of a patient with primary myelofibrosis?
- Leucoerythroblastic picture
- Tear drop poikilocytes
- Giant platelets
- Circulating megakaryocytes
What is a characteristic feature seen on bone marrow aspirate in primary myelofibrosis?
Dry tap
What might you see on histological analysis of a trephine biopsy in primary myelofibrosis?
- Increased reticulin and collagen fibrosis
- Prominent megakaryocyte hyperplasia and clustering
- New bone formation
Which mutations would you test for in a patient with primary myelofibrosis?
JAK2 and Calreticulin
NOTE: these are not diagnostic
What are some bad prognostic features in primary myelofibrosis?
- Severe anaemia
- Thrombocytopaenia
- Massive splenomegaly
NOTE: median survival is 3-5 years
Outline the treatment options for primary myelofibrosis.
- Supportive - RBC and platelet transfusions (usually ineffective becasue of splenomegaly)
- Hydroxycarbamide (may worsen anaemia)
- Ruxolitinib - JAK2 inhibitor
- Allogeneic stem cell transplantation
- Splenectomy - dangerous operation but may provide symptomatic relief
What might you expect to see in the FBC of a patient with CML?
- Leucocytosis (MASSIVE)
- Normal or raised Hb and platelets
What would you expect to see in abundance in the blood film of a patient with CML?
- Neutrophils
- Basophils
- Myelocytes (NOT blasts)
NOTE: myelocytes are immature myeloid cells that are NOT blasts (analogous to reticulocytes for red blood cells)
Briefly describe the natural history of CML before targeted treatment was available.
- 5-6 years stable phase
- 6-12 months accelerated phase
- 3-6 months blasst crisis
What is the Philadelphia chromosome?
CML is caused by a translocation between 9;22 producing a derivative chromosome, 22q, which is called the Philadelphia chromosome
What are the two genes that make up the fusion gene in the Philadelphia chromosome?
Bcr = breakpoint cluster region
Abl = ableson tyrosine kinase
Explain how this fusion gene results in excessive proliferation of myeloid cells.
- Abl is a tyrosine kinase that drives cell proliferation but is rarely expressed unless the cells are receiving a stimulus to proliferation
- Bcr 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
List some diagnostic techniques used to identify the CML and monitor response to treatment.
- 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
What are some issues associated with 1st generation Bcr-Abl tyrosine kinase inhibitors?
- 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)
List some examples of Bcr-Abl tyrosine kinase inhibitors.
- 1st generation: imatinib
- 2nd generation: dasatinib, nilotinib
- 3rd generation: bosutinib
What are the next steps in treatment if the first-line fails?
- 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
