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 with normal Hb and HCT (associated with alcoholism, obesity and diuretics)
True - caused by an excess of erythrocytes.
What are the two types of TRUE POLYCYTHAEMIA
Primary causes
- noted to have low EPO.
- Myeloproliferative neoplasms (malignant)
Secondary causes
- noted to have raised EPO
- no issue with bone marrow - simply being over-stimulated (which can be appropriate or inappropriate over-stimulation)
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 primary polycythaemia (or myeloproliferative neoplasms) be broadly categorised?
- Philadelphia positive: CML
- Philadelphia negative: polycythaemia vera, essential thrombocythaemia, primary myelofibrosis
What is the main clinical worry with polycythaemia - which patients are at increased risk of it
Main worry of polycythaemia = vaso-occlusive episode (e.g. stroke)
Pts with primary polycythaemia > secondary polycythaemia
What are the two main processes that cells undergo as they develop and how are these different in acute and chronic leukaemia?
- Two processes: differentiation + proliferation
- Chronic leukaemia: differentiation is intact (produces mature cells) + proliferation is excessive and abnormal due acquired mutation.
- 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 genes commonly associated with the development of myeloproliferative disorders affect which protein/molecular structure?
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
Outline the mutation seen in Polycythaemia Vera
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 constantly active even in the absence of EPO thereby driving cell replication constantly in the absence of a stimulus.
Outline the typical presentation of polycythaemia vera?
- Often incidental
- Hyperviscosity: headaches, visual disturbance, stroke, fatigue, dyspnoea, light-headedness
- Increased histamine release: aquagenic pruritis (itchiness when in warm water and warm environments), peptic ulceration
Note: commonest in men than women, more in elderly
List the investigation findings expected in polycythaemia vera (Hb, HCT, EPO levels, genetic testing)
Raised Hb
Raised HCT
Low serum EPO
Mutation Testing - JAK2 (V617F) +ve –> diagnostic in context with above!
Outline the principles of treatment of polycythaemia vera.
- Venesection (aim to reduce HCT to <45% and plts /< 400x109/L)
- Hydroxycarbamide (if venesection not effective to reach aims)
May consider aspirin to control thrombosis risk
What is essential thrombocythaemia?
Chronic myeloproliferative disorder mainly involving the megakaryocyte lineage
Characterised by sustained thrombocytosis > 600 x109/L
What mutations are seen in essential thrombocythaemia
60% = JAK2
30% = Calreticulin (CALR)
5% = MPL
Outline the typical presentation of essential thrombocythaemia.
- Incidental finding (50%)
- Thrombosis (arterial and venous) - CVA, TIA, DVT, PE, gangrene
- Bleeding (mucous membranes, cutaneous, menorrhagia) - as existing plts are dysfunctional
- Splenomegaly (modest)
List findings you’d expect in Essential Thrombocythaemia (bloods and blood film)
Plts >600x10^9
Blood film = large platelets + megakaryocyte fragments
Outline the treatment options for essential thrombocythaemia.
- Aspirin
- Hydroxycarbamide
- Anagrelide (specifically inhibits platelet function but rarely used because of side-effects (flushing + palpitations)
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 (excessive clone production stimulates reticulin and fibrouse tissue deposits in BM)
- Characterised by extramedullary haemopoeisis
- NOTE: other myeloproliferative disorders can transform into myelofibrosis
Outline the typical presentation of primary myelofibrosis.
- Cytopaenias (anaemia, thrombocytopaenia)
- Thrombosis - some pts have a proliferative phase where a cell line number may be increased
- MASSIVE splenomegaly
- Hepatomegaly
- Hypermetabolic state (FLAWS)
What might you expect to see in the blood film of a patient with primary myelofibrosis?
- Leucoerythroblastic picture = nucleated erythroblasts and immature leucocytes of neutrophilic myeloid lineage (due to infiltration of BM!)
- Tear drop poikilocytes
- Giant platelets
- Circulating megakaryocytes
What is a characteristic feature seen on bone marrow aspirate in primary myelofibrosis?
Dry tap
Which mutations would you test for in a patient with primary myelofibrosis?
JAK2 (60%) and Calreticulin (30%)
NOTE: these are not diagnostic
What are some bad prognostic features in primary myelofibrosis?
- Severe anaemia (< 100)
- Thrombocytopaenia (< 100)
- Massive splenomegaly at diagnosis
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 (if in proliferative phase but may worsen anaemia)
- Ruxolitinib - JAK2 inhibitor (for those with worse prognosis)
- Allogeneic stem cell transplantation (curative but too toxic for esp for elderly pts!)
- Splenectomy - dangerous operation as is main site of extramedullary haematopoeisis (which pt depends on) but may provide symptomatic relief
What might you expect to see in the FBC of a patient with CML?
- Leucocytosis (MASSIVE)
- Raised neutrophils, basophils!
- Normal or raised Hb and platelets
What would you expect to see in abundance in the blood film of a patient with CML?
Biphasic picture! (less mature myelocytes and mature end product cells!)
* 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
In haematological cancers what are the 3 types of mutations that can predispose to a haematological malignancy and give an example of each
Novel fusion oncoprotein
- translocation causes a novel fusion gene which acts as a oncogene hence a novel oncoprotein.
- seen in philadelphia chromosme with Bcr-ABL
Dysregulated expression of intact proto-oncogene
- mutations or translocations increase expression of existing but usually suppressed proto-oncogenes
- seen in lymphomas (e..g. follicular b cell lymphoma t(14;18) = bcl2)
Activating point mutation of tyrosine kinase
- mutation causes constant activation of a tyrosine kinase
- seen in JAK2 mutation in polycythaemia vera!
