Evolving Therapeutic Options for Polycythemia Vera: Perspectives of the Canadian Myeloproliferative Neoplasms (MPN) Group

Shireen Sirhan1, Lambert Busque2, Lynda Foltz3, Kuljit Grewal4, Caroline Hamm5, Nicole

Laferriere6, Pierre Laneuville7, Brian Leber8, Elena Liew9, Harold J. Olney10, Jaroslav

Prchal7, Anna Porwit11, Vikas Gupta12

Institution Affiliations: 1Division of Hematology, Jewish General Hospital, Montreal,

Quebec; 2Hematopoiesis and Aging Research Unit, Hôpital Maisonneuve-Rosemont,

Montreal, Quebec; 3Division of Hematology, St. Paul’s Hospital, University of British

Columbia, Vancouver, British Columbia; 4Faculty of Medicine, Memorial University, St.

John’s, Newfoundland; 5Western University, Department of Oncology, Windsor site;,

Windsor, Ontario 6Thunder Bay Regional Health Sciences, Department of Oncology,

Lakehead University, Thunder Bay, Ontario; 7Department of Oncology, McGill

University, Montreal, Quebec; 8Department of Medicine, Hematology and

Thromboembolism, McMaster University, Hamilton, Ontario; 9Division of Hematology,

University of Alberta, Edmonton, Alberta; 10Department of Hematology and

Transfusional Medicine, Centre Hospitalier de l'Université de Montréal, Montreal,

Quebec; 11Department of Pathology, University Health Network, Department of

Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario,12

Medical Oncology and Hematology, Princess Margaret Cancer Centre, University of

Toronto, Toronto, Ontario

Short Title: Treatment Options for PV

Word count:Abstract: 243 Main Manuscript: ~ 5430 References: 90

Tables: 4 Figures: 3

1

Corresponding author: Vikas Gupta, MD, FRCP, FRCPath; The Elizabeth and Tony

Comper MPN Program, Princess Margaret Cancer Centre, 610 University Avenue,

Toronto, ON, M5G2M9, Canada; Phone: 416-946-4521; Fax: 416-946-6546; E-mail:

vikas.gupta@uhn.ca

2

Conflicts of Interest

Vikas Gupta: Received research funding from Incyte and Novartis; received honorarium from Novartis/Incyte; and served on advisory board panel of Novartis.

Pierre Laneuville: Served on advisory board panel and as a speaker for Novartis.

Brian Leber: Received honorarium form Novartis and membership in medical advisory board.

Elena Liew: Received honorarium from Novartis and served on advisory board panel of Novartis.

Anna Porwit: Received honorarium from Novartis and served on advisory board panel of Novartis.

Shireen Sirhan: Received honorarium from Novartis and served on advisory board panel of Novartis.

Other authors declare no relevant conflict of interests.

3

Abstract

Polycythemia vera (PV) is a clonal stem cell disorder characterized by erythrocytosis

and associated with burdensome symptoms, reduced quality of life, risk of

thrombohemorrhagic complications, and risk of transformation to myelofibrosis (MF) and

acute myeloid leukemia (AML). The discovery of the JAK2 V617 mutation marked a

significant milestone in understanding the pathophysiology of the disease and,

subsequently, the diagnostic and therapeutic approaches. The current diagnostic

criteria for PV are based on hemoglobin level and presence of the JAK2 V617 mutation.

The treatment is geared toward prevention of thrombotic events, normalization of blood

counts, control of disease-related symptoms, and potentially prolonging survival.

Cytoreductive therapy is indicated in patients at increased risk of thrombosis.

Hydroxyurea (HU) remains the most commonly used first-line cytoreductive therapy and

is superior to phlebotomy in reducing risk of arterial and venous thrombosis. Interferon

(IFN) is used either at failure of HU or in selected patients as first-line therapy. The

results of pegylated IFN in phase 2 studies appear encouraging, with molecular

responses occurring in some patients. Ongoing phase 3 studies of HU vs. pegylated

IFN will define the optimal first-line cytoreductive therapy for PV. A recent phase 3 trial

has shown the superiority of JAK1/2 inhibitor, ruxolitinib in comparison to best available

treatment (BAT) in HU-intolerant or resistant patients. The therapeutic landscape of PV

is likely to change in the near future. In this report, we assess the potential impact of the

changing landscape of PV management on daily practice.

Key words: Polycythemia vera, JAK2 mutation, hydroxyurea, interferon, ruxolitinib

4

Introduction

Polycythemia vera (PV) is a clonal stem cell disorder characterized by overproduction of

red blood cells, often accompanied by leukocytosis and/or thrombocytosis.1 In 1951,

Dameshek speculated that the manifestations of proliferative activity of bone marrow

cells was due to an undiscovered myelostimulatory factor,1 which later was discovered

to be the JAK2 V617F mutation. Overactivity of JAK signaling caused by the unique

V617F mutation within exon 14 (~95% of PV)2 and by different mutations within exon 12

of the JAK2 gene (~4% of PV)3 has been implicated in the pathogenesis of PV.

Erythrocytosis is the most prominent clinical feature of PV and distinguishes it from

other myeloproliferative neoplasms (MPNs). Similar to other MPNs, individuals with PV

often have splenomegaly and significant burden of disease-related symptoms, including

pruritus, night sweats, fatigue, and bone pain. Patients are also at risk of thrombotic

complications and transformation to secondary myelofibrosis also known as post-

polycythemia vera myelofibrosis (PPV-MF) or acute myeloid leukemia (AML).

The estimated incidence of PV worldwide is about 0.84 per 100,000, with slightly higher

reported rates in Europe than in North America.4,5 Recent data from two large health

plans in the United States indicate the prevalence rates of 44 to 57 cases per 100,000.5

However, there is a wide variation in both prevalence and incidence estimates observed

across data sources. The median age at presentation is in the sixth decade and

approximately 10% of patients are under 40 years, with an equitable gender

distribution.6

The clinical presentation of PV usually involves the following three common scenarios:

1) an incidental discovery of elevated hemoglobin or hematocrit (Hct); 2) diagnosis after

a thrombotic event; and 3) diagnosis after investigating disease-related symptoms.7

These may be nonspecific complaints, such as headache, weakness, dizziness, and

excessive sweating, which are present in 30% to 50% of PV patients; acute gouty

arthritis has been described in 5% to 20%. Symptoms more specific to PV include

pruritus, especially after warm baths or showers (aquagenic pruritus; reported by 70% of

5

patients),8 and erythromelalgia, or a burning pain in the feet or hands accompanied by

erythema (seen in 28% of patients).9

The most common abnormal findings on physical examination in PV include

splenomegaly (present in about 30% to40% of patients), facial plethora (67% of

patients), and hepatomegaly (40% of patients). Laboratory findings include an elevated

hemoglobin/Hct in most patients, platelet count >450x109/L, and a white blood cell

(WBC) count >10.5x109/L in about 50% of patients.6

Diagnostic Approaches

Current diagnosis of PV is based on the 2008 World Health Organization (WHO) criteria

and requires the composite assessment of clinical and laboratory features, as

summarized in Table 1A.10 Although the WHO criteria are widely applied in clinical

practice, consensus for the optimal diagnostic criteria for PV has not yet been

achieved.11 Furthermore, the current WHO criteria are undergoing revisions proposed

changes are also outlined in Table 1A.12

The rational for the proposed changes is based on recent observations that some JAK2

V617F-positive PV patients present with hemoglobin levels lower than the current WHO

criteria of 185 g/L for men and 165 g/L for women.13,14 Compared to other PV patients,

masked PV (mPV) patients have increased risk of thrombosis, perhaps resulting from

late diagnosis, and inadequate disease control. As mPV patients are missed by current

WHO criteria, a retrospective analysis of a large cohort of MPN patients has suggested

that lowering the hemoglobin threshold to 165 g/L for men and 160 g/L for women would

capture most of these mPV cases.14

The Canadian MPN group acknowledges the necessity of appropriately diagnosing

mPV, but has concerns about potential misuse of these criteria for screening for PV, as

large numbers of individuals would be subjected to unnecessary further testing to rule

out mPV. To that end, two large Montreal hospitals (Centre Hospitalier de l'Université de

6

Montréal and Maisonneuve-Rosemont Hospital) performed an analysis (unpublished

results, manuscript in preparation) that showed that close to 4.4% of all complete blood

count (CBC) analyses from unselected male (non-hematology-oncology clinic) patients

had hemoglobin levels higher than 165 g/L vs. only 0.29% that meet current criteria

(hemoglobin higher than 185 g/L). This indicates that close to 15 times more males will

be suspected as having PV and will be subjected to further investigation. The proposed

change to the WHO criteria has less impact in females, as only 0.39% had hemoglobin

levels greater than 160 g/L. This is only five times more frequent than the current cut-off

of 165 g/L, which accounts for 0.07% of unselected females. Therefore, it is important

that the cost-effectiveness of the new proposed criteria be carefully evaluated before

they are adapted in routine clinical practice. In addition, hemoglobin levels above the

suggested threshold should not be taken in isolation, but rather in the context of other

potential signs and symptoms indicative of PV. It is important to emphasize that the

intent of lowering the thresholds is to more accurately differentiate between JAK2-

positive essential thrombocythemia (ET) and mPV rather than to serve as a base for

population screening.

For diagnostic purposes, a CBC is of particular relevance, as an increase in all three

lineages (erythrocytosis with leukocytosis and/or thrombocytosis) is more indicative of

PV than isolated erythrocytosis.15 In patients with isolated erythrocytosis, causes of

secondary polycythemia should be considered. The investigations for PV in suspected

cases should begin with peripheral blood screening for JAK2 V617F mutation (Figure 1

provides a proposed diagnostic algorithm).16 The laboratory detection of JAK2 V617F is

highly sensitive (97% sensitivity) and almost 100% specific for distinguishing PV from

other causes of increased Hct.17 The finding of the JAK2 V617F mutation, however, is

not specific for PV, since it is also present in a substantial proportion of patients with ET,

as well as primary myelofibrosis (PMF).18 The possibility of a false positive or false

negative mutation test result can be addressed by the concomitant testing of serum

erythropoietin (EPO) level, as more than 85% of patients with PV have low serum EPO

concentrations.19 Furthermore, EPO levels above normal are unusual for PV and

suggest secondary erythrocytosis, with a specificity of 98%.20 Low serum EPO levels in

7

the absence of JAK2 V617F require additional mutational analysis for JAK2 exon 12

mutations. 3,21

Bone marrow (BM) evaluation in JAK2 V617F-positive patients with erythrocytosis

provides limited additional value for diagnostic purpose and currently is not routinely

required.15,22 However, the proposed changes to the WHO criteria for the diagnosis of

PV mandates a BM biopsy with typical PV histology as one of three major criteria (Table

1B).12 Information regarding age-adjusted bone marrow cellularity and grade of fibrosis

may have prognostic value and, as such, help in optimizing therapeutic approaches.22 In

addition, a baseline BM biopsy might be essential in cases where the diagnosis is

unclear.

Approximately 11% of PV patients have cytogenetic abnormalities,6 including trisomy 8,

trisomy 9, 13q-, and 20q-.23 These abnormalities are not specific to PV, are more

common in older PV patients (>60 years of age)23, and increase in frequency with

disease progression and transformation.24 Earlier studies suggest that some of the

cytogenetic abnormalities may have prognostic value.25 To our knowledge, cytogenetic

studies are not routinely performed in PV patients in Canada.

Presently, there is no indication to test for genetic mutations other than those involving

the JAK-STAT pathway in the routine clinical management of PV. However, with the

wider availability of next-generation sequencing (NGS), there is an increasing interest to

investigate additional mutations in PV patients.26

Prognosis and Risk Assessment

Polycythemia vera is associated with a shortened life expectancy compared with the

general population.4,6,27 According to a large population-based study conducted in

Sweden, the relative survival rate for PV at 10 years is about 60%.27 Thrombosis, which

is much more common in PV than in the general population, is one of the major causes

of death.28 At PV diagnosis, arterial thrombosis is present in 16% to 27% and venous

thrombosis in 7% to 12% of patients, and the rate of thrombosis is 2% to 4% per year

8

over the course of the disease.28-31 Thus, because of the high prevalence and incidence

of this complication, risk-stratification of PV patients is typically based on the likelihood

of thrombotic risk rather than survival or risk of transformation to PPV-MF or AML.32 The

data indicate that individuals with a history of thrombosis or those who are 60 years of

age are considered at higher risk of thrombotic events.32,33 Table 2 provides an overview

of risk factors associated with thrombosis,28 overall survival,6 transformation to PPV-

MF,28,34 and AML.6,35 A risk-stratification model, based on a retrospective analysis of

1,545 PV patients, clearly delineated three distinct categories, with median survival

ranging from 10.9 years to 27.8 years.6

Goals of Therapy

The goals of therapy in PV are prevention of occurrence or recurrence of thrombosis,

control of Hct and normalization of other blood counts, and mitigation of disease-related

symptoms. By decreasing the risk of thrombosis survival is extended. Given the long

natural history of the disease, it is important to manage certain high-risk situations, such

as pregnancy and surgery, effectively. Patients should be counseled that current

approaches are aimed at maximizing benefits while minimizing potential risks, and are

non-curative.

Therapeutic Approaches

The European LeukemiaNet (ELN) guidelines for Philadelphia-Negative Classical MPNs

recommend that all patients with PV be managed with phlebotomy to maintain the Hct

below 45%, and low-dose Aspirin® to reduce risk of cardiovascular events.32 Although

phlebotomy has the advantage of immediately reducing the Hct, it does not decrease

the platelet or leukocyte count due to the short half-life of these cells. Thus,

cytoreduction is recommended in patients at high risk for thrombosis. Figure 2 provides

a suggested algorithm for the frontline management of PV based on patient risks and

symptoms.

Control of Cardiovascular Risk Factors

9

Currently, there are no data informing lipid or blood pressure target ranges specifically

for individuals with PV. However, with the increased risk of arterial thrombosis, it is

prudent to manage atherosclerotic risk factors (including hypertension, hyperlipidemia,

diabetes) and encourage smoking cessation. Clinicians should refer to the Framingham

Heart Study and the risk assessment tool incorporated into Canadian guidelines for

general prevention of cardiovascular disease (Figure 3).36

Phlebotomy

Phlebotomy, recommended by Osler at the beginning of the 20th century,37 has

remained the mainstay of the treatment for PV for the past 100 years. A randomized

trial conducted by the Polycythemia Vera Study Group (PVSG) in 1967 compared

phlebotomy alone with phlebotomy combined with myelosuppressive therapy

(chlorambucil or P-32).38 Although the incidence of thrombosis in the first three years

was higher in the phlebotomy-only arm, these patients had a significant overall survival

advantage. The difference in survival was attributed to an increased incidence of AML in

patients treated with chlorambucil or P-32 compared to those treated with phlebotomy

alone.

Based on several studies, the recommended Hct target is <45%.30,32 A retrospective

study demonstrated a progressive increase in the incidence of vascular complications at

Hct levels higher than 44%.39 This is also supported by laboratory studies showing

impaired cerebral blood flow at higher Hct levels.40 Some experts recommend Hct target

<42% in women. The lower Hct target in women was derived from the physiological

difference between genders and not from direct evidence.41 The European Collaboration

on Low-Dose Aspirin in Polycythemia Vera (ECLAP) trial,33 a large, double-blind,

placebo-controlled, randomized study that assessed the safety and efficacy of

prophylaxis with low-dose Aspirin® in 518 patients with PV, did not demonstrate

differences in the incidence of thrombosis across a range of Hct levels between 45%

and 50%. However, a recent study conducted by the Cytoreductive Therapy in

Polycythemia Vera (CYTO-PV) Collaborative Group suggested that maintaining a Hct

10

target of <45%, as compared with a target of 45% to 50%, was associated with a

significantly lower rate of thrombotic events without an increase in serious treatment

complications.30 After 31 months, the composite endpoint of time until death from

cardiovascular causes or a major thrombotic event was reached in 2.7% of patients in

the low Hct group vs. 9.8% in the high Hct group. Despite being the only randomized

study assessing the effect of the intensity of Hct control on thrombosis, the CYTO-PV

trial has several limitations. For example, patients in the high-Hct group also had

significantly higher leukocyte counts compared to those in the low-Hct group. Since it

has been suggested that a higher leukocyte count maybe associated with an increased

risk of thrombosis, this may confound the results. In addition, the study only accrued

about 1/3 of the planned number of patients, therefore, overestimation of the effect size

due to chance cannot be ruled out.

Based on available data, Hct target <45% is the widely accepted standard of care in

routine clinical practice.

Although inconvenient, phlebotomies are usually well-tolerated. Some patients might

experience fatigue after the procedure; this might be managed by adequate hydration.

Frequent phlebotomies lead to iron deficiency, abnormal red blood cell (RBC)

morphology, and eventually reactive thrombocytosis. Rarely, phlebotomy-induced iron

deficiency might lead to complications such as cognitive problems and restless leg

syndrome.42,43

Antiplatelet Drugs and Anticoagulants

The randomized, placebo-controlled, ECLAP study demonstrated a significant risk

reduction in a combined endpoint of cardiovascular and venous thrombotic events (RR

0.40) with the use of low-dose Aspirin® (100 mg daily) over placebo, with no increased

risk of bleeding.33 Based on this data, daily low-dose Aspirin® is recommended for all PV

patients in the absence of contraindications.32 Patients presenting with acute arterial or

venous thrombotic events should receive acute antithrombotic therapy, as per general

thrombosis management recommendations.44 For venous thrombosis (VTE), treatment

11

with low-molecular-weight heparin (LMWH), followed by warfarin is favored. There is

lack of clinical data on use of novel oral anticoagulants (NOACs) in patients with PV and

these agents are not recommended in routine practice at this stage. Based on the

Randomized Comparison of Low-Molecular-Weight Heparin vs. Oral Anticoagulant

Therapy for the Prevention of Recurrent Venous Thromboembolism in Patients with

Cancer (CLOT) study,45 where the risk of VTE was almost reduced to half for patients

treated with LMWH without increase in bleeding complications, general thrombosis

guidelines recommend the use of LMWH over LMWH/warfarin for treatment of

malignancy-associated VTE.44 However, one should keep in mind that PV patients were

not included in the CLOT study.45

Overall, there is no consensus regarding the optimal duration of anticoagulation in PV

patients following an initial thrombotic event, leading to a broad diversity of clinical

practices in duration and type of anticoagulation agents prescribed;46 however,

thrombosis in patients with PV has a high recurrence rate of about 7.6% per year.47 On

the other hand, the occurrence of major bleeding is <1% per year for warfarin or

Aspirin®, but increases to 2.8% per year for combination therapy.47 After the first venous

thrombotic event, long-term oral anticoagulation was associated with a 63% reduction in

the risk of recurrence without a significant increase of the incidence of major bleeding.

Given the high rate of recurrence of thrombosis, an individualized approach for long-

term anticoagulation use is recommended after careful consideration of patient risk

factors. This is in accordance with recently published German and Austrian consensus

guidelines that recommend an individualized risk-benefit assessment after three to six

months of anticoagulation therapy in patients who experience a thrombotic event.48

According to these guidelines, Aspirin® is a reasonable option after three to six months

of warfarin and cytoreduction in patients with VTE at initial diagnosis. Long-term

anticoagulation may be favored in patients with high-risk features (recurrent, splanchnic,

or life-threatening VTE) and low bleeding risk.

Cytoreductive Therapy

12

The high risk of thrombosis (>60 years of age and/or prior history of thrombosis) is the

main indication for cytoreductive therapy (Figure 2).32 In addition, cytoreductive therapy

can be considered on an individual case basis (irrespective of risk) in patients with any

of the following features:

a. Extreme thrombocytosis with platelet count 1500x109/L

b. Progressive leukocytosis 25x109/L

c. Symptomatic splenomegaly

d. Severe disease-related symptoms

e. Intolerance to phlebotomy, especially in patients with compromised cardiac

function, inability to comply with phlebotomy requirements, or poor venous

access

Optimal Cytoreductive Therapy

First-line Agents

Although the ELN guidelines recommend either hydroxyurea (HU) or interferon (IFN)-

as first-line cytoreductive therapy at any age, these guidelines also state that HU should

be used with caution in young patients (i.e., age <40 years).32

Hydroxyurea

Hydroxyurea is an oral antimetabolite that prevents DNA synthesis by inhibiting the

enzyme ribonucleoside reductase. In the PVSG trial, patients treated with HU had lower

incidence of thrombosis compared to historical controls treated with phlebotomy (9.8%

vs. 32.8%).49 In randomized trials that compared HU with pipobroman, the incidence of

thrombotic events was similar between the treatment arms (Table 3A).50,51

Hydroxyurea as Mutagen: Myths vs. Scientific Data

A potential hazard in using HU is a mutagenesis as a consequence of the role of

ribonucleotide reductase in DNA repair. The clinical significance of this has been

scrutinized closely in the treatment of MPNs, but with varying interpretations due to the

inherent risk of leukemic progression in PV even when untreated (Table 3B). While

13

some studies have reported higher rates of leukemia transformation with HU compared

to controls (6% with HU vs. 1.5% with phlebotomy after a median follow-up of 8.6

years),49 Finazzi et al35 reported that patients with PV have an increased risk of leukemia

only if they are >70 years of age (hazard ratio [HR] 4.30) or if they use cytoreductive

agents (i.e., P32, busulphan, and pipobroman) other than HU or interferon (HR 5.46).

By comparison, the use of HU in a non-malignant blood disorder, sickle cell disease in

children, does not increase the risk of myelodysplastic syndrome (MDS)/AML.52

Based on this perceived risk-benefit ratio, HU is widely used for the treatment of PV in

Canada and is usually well-tolerated. The starting dose of HU is 500 mg/day, with dose

increases until the desired response is obtained. When selecting an appropriate dose of

HU, the clinician should consider the extent of myeloproliferation (higher doses in cases

of leukocytosis, thrombocytosis, and splenomegaly), symptom burden, and the patient’s

ability to tolerate higher doses. Female patients should be advised that HU is

contraindicated in pregnancy and, therefore, appropriate contraceptive precautions

should be taken.

HU Resistance or Intolerance

Although not a common problem in PV, the development of HU resistance or

intolerance needs to be further examined, especially with the availability of other

treatment options. A survey of 3,411 MPN patients treated with HU found a 5%

incidence of significant non-hematologic side effects, with gastrointestinal or cutaneous

problems accounting for 90% of events.53

In order to assist clinicians facing the decision to discontinue HU and move on to the

second-line therapies, an ELN panel of experts has developed a standardized definition

of resistance and intolerance to HU in PV (Table 4).54 It is noteworthy that these

definitions are based on expert opinion and have limited validation. When applying

these criteria to a cohort of 261 HU-treated PV patients, resistance and intolerance

were reported in 11% and 13% of patients, respectively, after a median 4.4 years of

therapy.55 The study also found HU resistance to be associated with shorter survival

14

(median 5.2 years compared to >20 years for non-resistant patients) and higher risk of

transformation to PPV-MF or AML (HR,6.8; 95% CI, 3.0%-15.4%; P <0.001).56 It should

also be noted that HU has limited efficacy in relieving some PV-related symptoms, such

as aquagenic pruritus.56

Interferon

Both short-acting and pegylated IFN-α are effective in controlling blood counts in most

patients,57 and may be considered first-line therapy, particularly in younger patients.32

IFN represents an effective alternative to HU, having a slower onset of Hct control as

well as a different toxicity profile than HU.

Apart from the absence of leukemogenic risk, the other benefit of IFN may be better

disease control and improvement in symptoms, including pruritus. A small French study

has demonstrated that IFN reduces the size of the malignant clones measured by JAK2

allele burden58 and may retard or reverse fibrosis.59 Furthermore, this benefit is

sometimes sustained after treatment discontinuation. For these reasons, it is widely

used in some European jurisdictions. In Canada, the coverage by provincial

reimbursement plans for primary treatment of PV varies between provinces.

IFN is commonly administered subcutaneously at a starting dose of 3 million units daily

and pegylated IFN is given at a starting dose of 45-90 g weekly. The dose should be

titrated individually based on efficacy and toxicity.

Many patients experience flu-like symptoms initially. These can be controlled with

hydration and premedication with acetaminophen. Side effects, including autoimmune

disorders, flu-like manifestations, depression, heart and ocular disease, lead to

permanent discontinuation in 20% to 40% of patients on conventional and 20% to 25%

on pegylated IFN.57

Interferon vs. HU

15

Although there is some suggestion that IFN- might have potential benefits over HU, a

firm conclusion cannot be made at the present time due to the absence of comparative

data in controlled settings. Furthermore, a comprehensive comparison with HU must

determine the long-term safety, tolerability, and durability of response (hematologic,

cytogenetic, and molecular) to IFN, as well as provide firm evidence about the effect on

reducing the risk of thrombosis and improving survival.60

Ongoing randomized trials comparing HU with interferon will be critical in defining the

future role of IFN in management of PV patients (DALIAH trial; NCT01387763).

Other Therapies

Other agents helpful in specific circumstances include busulfan and anagrelide.

Busulfan is an alkylating agent. Its use in PV was studied in a randomized clinical trial

conducted between 1967 and 1978 by the European Organization for Research on

Treatment of Cancer (EORTC).61 The trial randomized 293 PV patients to

radiophosphorus or oral busulfan. Treatment with busulfan resulted in long-term clinical

and hematologic responses and superior 10-year overall survival (70% vs. 55%).61

Furthermore, at a median follow-up of 8 years, there was no significant difference in the

risk of leukemic transformation, non-hematologic malignancy, or transformation into

PPV-MF between the two treatments. Favorable outcomes with oral busulfan have also

been reported in single-arm studies.62,63 Recently, Kutiakose, et al determined that in

addition to rapid and sustained hematologic responses, busulfan also decreased the

JAK2 V617F allele burden in patients refractory to multiple therapies, including HU.64

Side effects of busulfan include hyperpigmentation, protracted pancytopenia, and rare

cases of pulmonary fibrosis. There is some concern regarding drug leukemogenicity,35

although this has not been proven in a controlled study in PV.6 The agent has been

demonstrated to be safe for short-term use in the elderly population, where the

recognized risk of increased AML transformation with prolonged use may not be

clinically relevant.65

16

Because of possible prolonged and delayed myelosuppression, the dose of busulfan

needs to be carefully titrated. A starting dose of 2-4 mg daily until target Hct is reached

is commonly used. Many patients maintain a hematologic response despite

discontinuing busulfan, and may only require a two- to three-week course every four to

six months.

Therefore, busulfan may be a reasonable option in some circumstances, such as elderly

patients who are refractory or intolerant to HU.61-65

Anagrelide disrupts the post-mitotic phase of megakaryocyte development by an

unknown mechanism. It is effective at lowering the platelet count without affecting other

cell lineages.66 Its use is restricted to decreasing the platelet count where this causes

ongoing symptoms and HU is ineffective or not tolerated.

Emerging Data on Ruxolitinib

Overactive JAK-STAT signaling resulting from gain-of-function mutations of JAK2 are

causally linked to pathogenesis of PV.67 Ruxolitinib is a JAK1/JAK2 inhibitor that has

demonstrated clinical benefit in patients with myelofibrosis.68,69

A phase 2 study in patients with advanced PV demonstrated that ruxolitinib was well-

tolerated and effective in controlling Hct, reducing splenomegaly, and improving

disease-related systemic symptoms.70 Following these encouraging results, a

prospective, randomized, open-label phase 3 study of ruxolitinib in PV patients resistant

to or intolerant of HU, the RESPONSE trial (NCT01243944), compared ruxolitinib to

investigator-determined best available therapy (BAT).71 Patients refractory to or

intolerant of HU were randomized to ruxolitinib (n=110) at a starting dose of 10 mg twice

daily which could be titrated up to a maximum of 25 mg twice daily, or BAT (n=111).

BAT included monotherapy with HU (59%), IFN/pegylated IFN (12%), anagrelide (7%),

pipobroman (2%), immunomodulatory drugs (IMIDs; 4%), or observation (15%). At

week 32, patients in the BAT group could crossover to ruxolitinib if they failed to meet

the primary endpoint or had disease progression. The primary endpoint was a

17

composite of Hct control (absence of phlebotomy need between weeks 8 to 32) and

spleen volume reduction 35% from baseline to week 32. This was achieved by 21% of

patients in the ruxolitinib group vs. 1% of those in the BAT group (OR 28.64; 95% CI

4.50-1206; P <0.0001). At week 48, the primary response was sustained in 91% of

patients, which was a secondary endpoint of the study. Another key secondary endpoint

was the proportion of patients who, at week 32, achieved complete hematologic

response (CHR) (defined as Hct control, platelet count ≤400 × 109/L, and WBC count

≤10 × 109/L). This was achieved by 23.6% in the ruxolitinib group compared to 8.9% in

the BAT group (OR 3.19; 95% CI 1.37-7.79; P=0.0034).

Ruxolitinib was also superior to BAT in achieving spleen volume reduction, as well as

improving PV-related symptoms, as assessed by the Myeloproliferative Neoplasm

Symptom Assessment Form (MPN-SAF). Interestingly, fewer thrombotic events

occurred in the ruxolitinib group (1 vs. 6 in the BAT group). At a median follow-up of 81

weeks, 85% of patients randomized to ruxolitinib continued therapy. Of those

randomized to BAT, 83.9% crossed over to the ruxolitinib arm after week 32.

The most commonly reported non-hematologic adverse events (AEs) were headache,

diarrhea, and fatigue; these were largely low-grade. The most common hematologic

AEs were anemia and thrombocytopenia; however, no patients discontinued treatment

due to these cytopenias. Similar to observations made in trials in myelofibrosis, herpes

zoster infection was more common in the ruxolitinib group (~6%).

The results of the RESPONSE trial subsequently led to FDA approval of ruxolitinib in

patients with PV who are resistant or intolerant to HU.72 The agent is currently

undergoing the Health Canada approval process.

Novel Investigational Agents in PV

18

The last few years have seen an explosion of knowledge in the understanding of the

molecular genetics of MPN, resulting in increasing interest in new investigational

therapies. Several groups of new drugs are being investigated in PV.

Interferon Therapy

Based on encouraging phase 2 data with pegylated IFN-α2a (Pegasys) with CHR in

range of 75% to 95% (including complete molecular response in 15% to 20% of

patients),57,58 further phase 3 studies are in progress. The Myeloproliferative Disorder

Research Consortium (MPD-RC) 112 trial (NCT01259856) will examine the role of

Pegasys as front-line cytoreductive therapy in patients with PV in comparison to HU.

Another study from the MPD-RC consortium (NCT01259817) will evaluate Pegasys as

salvage therapy in PV patients.

Encouraging phase 2 results using a longer-acting preparation (q 14 days) of another

peg-IFN α-2b (AOP-14)73 support further development of AOP-14 in PV, and another

randomized trial (PROUD-PV trial; NCT02218047) is in progress.

JAK Inhibitor Therapy

After the success of JAK inhibitors in MF patients, several JAK inhibitors have been

investigated in PV, some of which have been discontinued from further development

due to either toxicity or lack of efficacy (fedratinib, momelotinib, lastarutinib, XL-019).

To investigate other patient populations not included in the RESPONSE trial, further

studies using ruxolitinib are in progress.

Histone Deacetylase Inhibitors (HDACi)

Based on the pre-clinical rationale of epigenetic deregulation in MPN pathogenesis,

deregulation of HDAC genes, and the potent inhibitory activity on the autonomous

proliferation of JAK mutation-positive PV/ET, several HDACi have been investigated in

PV patients.74,75

Givinostat

19

Building on preliminary observations of responses (58%) in 12 PV patients with

givinostat as a single agent,74 a further study investigated two doses of givinostat

(50 mg and 100 mg) in combination with maximum tolerated dose of

hydroxycarbamide therapy (HC).75 Responses according to ELN criteria76 were seen

in 55% and 50% of patients, respectively. This drug was particularly effective in

reducing pruritis.

Vorinostat (MK-0683)

In an open-label, phase 2 study, vorinostat was investigated in 44 patients with PV

who were intolerant to previous therapies.77 Although it was effective in normalizing

elevated leukocyte and platelet count and symptoms related to pruritis and

splenomegaly, this medication was associated with high discontinuation rates due

to adverse events. No significant decrease in JAK2 V617F allele burden was

observed. Studies investigating lower doses of vorinostat in combination with

conventional or novel agents are planned in the future.

Combination Therapy

Currently, several concepts based on rationale designs, such as interferon with JAK

inhibitor therapy, interferon with p-53 MDM inhibition,78 and other rationale

combinations are being explored.

Specific Situations

Splanchnic vein thrombosis (SVT) is strongly associated with MPN. The prevalence of

MPN is 40.9% in patients with Budd Chiari syndrome and 31.5% in patients with portal

vein thrombosis,79 emphasizing the importance of a thorough investigation for MPN

including JAK2 V617F testing in patients with otherwise unexplained SVT. Medical

treatment of SVT includes LMWH followed by lifelong oral anticoagulation (to keep the

international normalized ratio [INR] between 2.0 and 3.0).15,44

20

Patients with PV are also at increased risk of perioperative thrombosis, with rates of

venous and arterial thrombosis of 7.7% and 1.1%, respectively. Hemorrhagic events,

mostly due to acquired von Willebrand’s syndrome, are reported in 7.3% of patients.80

Thus, perioperative optimization of cytoreductive treatment for adequate control of Hct

and platelet count is essential. In addition, deep venous thrombosis (DVT) prophylaxis

is recommended, especially in high-risk surgery. Aspirin® should be discontinued one

week prior to elective interventions, if the patient’s cardiovascular status permits.48

Pregnancy

Given the advanced median age of patients with PV, pregnancy is a rare event and,

therefore, the literature concerning its optimal management is sparse; recommendations

are based mostly on expert opinion and case series.81 It is important to keep in mind

that even in healthy women, pregnancy still has a recognized complication rate.

Nevertheless, pregnancy in PV is complicated by further increase in thrombotic and

bleeding complications, as well as pregnancy loss. The largest report on pregnancy in

PV comes from a single-center case series and included 18 pregnancies in eight

women.82 Based on their experience, the authors recommended tight Hct control with

phlebotomy and low-dose Aspirin® throughout the pregnancy, as well as LMWH

prophylaxis for six weeks post-partum. In addition, uterine artery Doppler examinations

at 20 and 24 weeks to obtain an assessment of placental function are recommended.

Patients with previous thrombosis or pregnancy complications (i.e., >3 first trimester

losses, or >1 second or third trimester pregnancy loss, stillbirth or preeclampsia, and

patients with a platelet count >1500x109) are considered at a higher risk. In the above

series, these patients were also treated with IFN for Hct and platelet count control.82 This

approach increased the chances of a live birth and decreased the risk of both maternal

and fetal complications.

IFN is also indicated in patients who have a prior requirement for cytoreduction. It

should be emphasized that teratogenic drugs, such as HU or anagrelide, should be

stopped prior to conception, with a three- to six-month washout period.83

21

Transformation of the Disease

Approximately 10% of PV patients transform into PPV-MF, with progressive

splenomegaly, MF-related symptoms, and anemia.84 MF evolution is difficult to foresee,

although leukocyte count >15x 109/L and allele burden >50% predicted a higher risk of

evolution to post-PV MF.34,84 In addition, PV patients with bone marrow fibrosis at

diagnosis have an approximately three-fold higher risk of developing PPV-MF than

those without.85 The diagnosis of PPV-MF is based on International Working Group for

Myelofibrosis Research and Treatment (IWG MRT) criteria (Table 1B)86 and PPV-MF is

managed as primary MF tailoring treatment to anemia, splenomegaly, and constitutional

symptoms. Following progression of PV to PPV-MF, survival is predicted using the

International Prognostic Scoring System (IPSS) at diagnosis87 and Dynamic IPSS

(DIPSS) at the follow-up assessments,88 although these risk scores were not specifically

validated in PPV-MF.

Evolution to AML is rare, and predictive factors are not well known.35 The risk of

leukemic transformation has been reported at 2.3% at 10 years and 5.5% at 15 years,

with older age, abnormal karyotype, and leukocytes 15 X 109/L as risk factors.6 Post-

PV-AML is an aggressive disease with very poor outcomes. Intensive chemotherapy

has a limited role in management unless further consolidated by allogeneic transplant.89

Hypomethylating agents and/or experimental therapies should be considered.90

Summary

Given the long natural history of PV and an increased risk of thrombosis, it is important

that these patients are appropriately managed and followed on a regular basis. Shared-

care models between centers with MPN expertise and community healthcare providers

are being explored in Canada. These models provide access to expert centers while

routine clinical care is provided in the community. Therapy should be individualized in

every patient and adjusted based on disease burden. as well as patient individual needs

and preferences.

22

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31

Tables and Figures

Table 1. Criteria for Diagnosis of PV

1A. Current and Proposed WHO Criteria for Diagnosis of PV

2008 WHO Diagnostic Criteria for PV10

2014 Proposed Revision of WHO Diagnostic Criteria for PV12

Major Criteria

1. Hemoglobin >185 g/L (men), >165 g/L (women), or evidence of increased red cell volume*

1. Hemoglobin >165 g/L (men), >160 g/L (women) or hematocrit >49% (men) >48% (women)

2. Presence of JAK2 V617F or other functionally similar mutation (e.g., JAK2 exon 12 mutation)

2. Bone marrow findings consistent with WHO criteria with pleomorphic megakaryocytes

3. Presence of JAK2 mutation

Minor Criteria

1. BM biopsy showing hypercellularity for age with trilineage myeloproliferation

1. Subnormal serum erythropoietin level

2. Serum erythropoietin level below the normal reference range

3. Endogenous erythroid colony formation in vitro

The diagnosis of PV requires meeting either both major criteria and 1 minor criterion or the first major criterion and 2 minor criteria.

*Hemoglobin or hematocrit >99th percentile of method-specific reference range for age, sex, altitude of residence, or hemoglobin >170 g/L in men, 150 g/L in women if associated with a documented and sustained increase of at least 20 g/L from a person’s baseline value that cannot be attributed to correction of iron deficiency, or elevated red cell mass >25% above mean normal predicted value.

Diagnosis of PV requires meeting either all three major criteria or the first two major criteria and one minor criterion.

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Abbreviations: PV = Polycythemia vera; WHO = World Health Organization Adapted from: Tefferi A, et al. Leukemia. 2014;28(7):1407-1413; and Thiele J, et al. Lyon, France: IARC Press:2008:40-43.

Table 1B. Diagnostic Criteria for PPV-MF86

Required CriteriaDocumentation of a previous diagnosis of PV as defined by WHO criteria

Bone marrow fibrosis grade 2-3 (on 0–3 scale) or grade 3-4 (on 0-4 scale)

Additional Criteria (Two are required)Anemia or sustained loss of requirement of either phlebotomy (in the absence of cytoreductive therapy) or cytoreductive treatment for erythrocytosisA leukoerythroblastic peripheral blood pictureIncreasing splenomegaly defined as either an increase in palpable splenomegaly of ≥5 cm (distance of the tip of the spleen from the left costal margin) or the appearance of a newly palpable splenomegalyDevelopment of ≥1 of three constitutional symptoms: >10% weight loss in six months, night sweats, unexplained fever (>37.5oC)

Abbreviations: PV = Polycythemia vera; WHO = World Health Organization Adapted from: Barosi G, et al. Leukemia. 2008;22(2):437-438.

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Figure 1. Proposed Algorithm for PV

The investigations for PV should begin with screening for JAK2 V617F mutation and testing of serum erythropoietin levels. This should be followed by mutational analysis for JAK2 exon 12 mutations in V617F-negative patients with subnormal serum erythropoietin levels. Currently, routine bone marrow evaluation in JAK2 V617F-positive patients is not required.

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Suspected PV

Elevated hemoglobin/hematocrit +/- History of thrombosis

Blood JAK2V617F/Erythropoietin screen

JAK2V617F-positive JAK2V617F-negative

Polycythemia Vera High erythropoietinLow erythropoietin

Screen for JAK2exon 12 mutation

Not PV, carefully evaluate for secondary causes of

erythrocytosisBone marrow

biopsy*Needed to confirm PV in JAKV617F-negative cases

*A diagnosis of PV can be made without bone marrow biopsy if a patient meets the criteria for an increase in red blood cell volume (as defined in the 2008 WHO guidelines) and is JAK2 V617F / Exon 12 mutation-positive. Using less stringent hemoglobin level criteria mandate bone marrow biopsy. Further, biopsy is highly recommended since degree of fibrosis and cytogenetic analysis can carry valuable prognostic information

Clinical clues: Splenomegaly, thrombosis, aquagenic pruritus, and erythromelalgia

Laboratory clues: Thrombocytosis, leukocytosis, and increased leukocyte alkaline phosphatase score

Abbreviations: PV = Polycythemia veraAdapted from: Tefferi A. Am J Hematol. 2013;88(6):507-516.

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Table 2. Risk Factors Associated with Thrombosis, Overall Survival, and Transformation to PPV-MF or AML

Risk Factor Hazard Ratio (95% Confidence interval [CI]) P-value

Thrombosis28

Age >65 (without prior thrombosis) 1.96 (1.29-2.97) P=0.0017History of thrombosis (patients < 65) 2.00 (1.22-3.29) P=0.0061Age > 65 years with prior thrombosis 4.35 (2.95-6.41) P<0.0001

Overall Survival*6

Age >61 7.4 (3.9-14.1) P<0.0001Leukocytosis (>10.5x109/l) 3.3 (1.8-6.1) P=0.0001History of venous thrombosis 3.9 (1.9-8.2) P=0.0002Abnormal karyotype 3.1 (1.6-5.8) P=0.0005

Transformation to PPV-MFJAK2 allele burden34 1.05 (1-1.1) P=0.03Disease duration >10 years28 15.24 (4.22-55.06) P<0.0001

Transformation to AMLAge >61*6 6.3 (1.8-22) P=0.004Abnormal karyotype*6 3.9 (1.2-13.1) P=0.03Leukocyte count 15X109/L*6 3.9 (1.3-11.6) P=0.01Exposure to P32, busulfan, and pipobroman35

5.46 (1.84-16.25) P=0.0023

*Multivariable analysis; karyotype included as a covariate (n=383)

Abbreviations: AML = acute myeloid leukemia; PPV-MF = post-polycythemia vera myelofibrosisAdapted from: Marchioli R, et al. J Clin Oncol. 2005;23(10):2224-2232; Passamonti F, et al. Leukemia. 2010;24(9):1574-1579; and Tefferi A, et al. Leukemia. 2013S;27(9):1874-1881.

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Figure 2. Management of PV

Patients with PV are managed according to their risk stratification. In addition to low-dose Aspirin® and phlebotomy, patients at high risk of thrombosis required cytoreductive therapy.

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Low-riskAge <60 years and no history of thrombosis

1. Cardiovascular risk factors modifications to prevent thrombotic complications

2. Low-dose Aspirin® to reduce risk of cardiovascular events3. Phlebotomy to control erythrocytosis by maintaining hematocrit

<45%

High-risk Age >60 years and/or

prior thrombosis

Cytoreduction

* If hydroxyurea and/or IFN-α-resistant/intolerant** If not used front-line

Front-lineHydroxyureaINF-

Second-line* Hydroxyurea or INF-** Ruxolitinib Busulfan, anagrelide,

participation in clinical trials

Risk Stratification

Progressively increasing leukocyte and/or platelet count

Enlarging spleen Uncontrolled disease-

related symptoms Poorly tolerated

phlebotomy

Abbreviations: INF = interferonAdapted from: Barbui T, et al. J Clin Oncol. 2011;29(6):761-770.

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Figure 3. Cardiovascular Risk Assessment

In addition to control of hematocrit and blood cell count, all patients with PV should be screen for cardiovascular risk factors.

Abbreviations: BMI = body mass index; COPD = chronic obstructive pulmonary disease; CVD = cardiovascular disease; eGFR = estimated glomerular filtration rate; HDL = high-density lipoprotein; LDL = low-density lipoprotein; TG = triglyceride.

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Framingham risk score 5%Repeat every year

Framingham risk score <5%Repeat every 3-5 years

For all: History and examination, LDL, HDL, TG, non-HDL (will be calculated from profile), glucose, eGFR

Optional: apoB (instead of standard lipid panel), urine albumin:creatinine ratio (if eGFR <60, hypertension, diabetes)

How to screen

Inflammatory diseaseHIV infection

COPDClinical evidence of atherosclerosis

or abdominal aneurysmClinical manifestation of

hyperlipidemiaObesity (BMI >27)

Current cigarette smokingDiabetes

Arterial hypertensionFamily history of premature CVDFamily history of hyperlipidemia

Erectile dysfunctionChronic kidney disease

Men 40 years of age and women 50 years of age or post-menopausal (consider earlier in ethnic groups at increased risk, such as South Asians or First

Nations individuals)

OR

All patients with the following conditions, regardless of age

Who to screen

Adapted from: Anderson TJ, et al. Can J Cardiol. 2013;29(2):151-167.

Table 3. Hydroxyurea: Benefits and Potential Long-term Consequences

Table 3A. Efficacy in Preventing Thrombosis49-51

Investigator Number, and Follow-up

Intervention Comparator Thrombosis Rates

PVSG 08 51 patients Hydroxyurea(prospective)

Phlebotomy(134 historical controls)

HU: 9.8%*Phleb: 32.8%*

Najean et alFPSG

292 pts(<65 yrs)7rs

HU(randomized)

Piprobroman No significant difference

Kiladjian et alFPSG

285 pts16 yrs

HU(randomized)

Piprobroman No significant difference

*On study events; all events, first 378 weeks—13.7% vs. 38.1%

Adapted from: Fruchtman SM, et al. Semin Hematol. 1997;34:17-23; Kiladjian JJ, et al. J Clin Oncol. 2011;29:3907-3913; and Najean Y, et al. Blood. 1997; 90:3370-3377.

Table 3B. Potential Long-term Consequences 6,35, 49,51,

Investigator Number, and Follow-up

Intervention Comparator AML/MDS

PVSG 08 51 patients15.2 yrs

Hydroxyurea(prospective)

Phlebotomy HU: 6% vs. Phleb: 1.5%* (NS)(9.8% all event)

Finazzi et alECLAP

1638 pts2.8 yrs(4,393 pt-yrs)

Observational No association with single-agent HU

Kiladjian et alFPSG

285 pts16 yrs

HU(randomized)

Piprobroman 10, 15, 20 yrsHU: 6.6, 16.5,

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(2011) (<65 yrs) 24.2%PIP: 13.1, 34.1, 52.1%

Tefferi et al(2013)

1,545 pts6.9 yrs

Retrospective No association with single-agent HU

*On study-event, 795 weeks

Abbreviations: AML = acute myeloid leukemia; HU = hydroxyurea; MDS = myelodysplastic syndromes; NS = non-significant; PIP = piprobroman Adapted from: Finazzi G, et al, Blood. 2005;105:2664-2670; Fruchtman SM, et al. Semin Hematol. 1997;34:17-23; Kiladjian JJ, et al. J Clin Oncol. 2011;29:3907-3913; andTefferi A, et al. Leukemia. 2013;27:1874-1881.

Table 4. Resistance/Intolerance to Hydroxyurea in PVa,55

Any of the following European LeukemiaNet (ELN) definitions

1. Need for phlebotomy to keep hematocrit <45%

2. Uncontrolled myeloproliferation, i.e., platelet count >400x109/L AND white blood cell count >10x109/L

3. Failure to reduce massive splenomegalyb by more than 50% as measured by palpation, OR failure to completely relieve symptoms related to splenomegaly

4. Absolute neutrophil count <1.0x109/L OR platelet count <100x109/L or hemoglobin <100 g/L at the lowest dose of hydroxyurea required to achieve a complete or partial clinico-hematological responsec

5. Presence of leg ulcers or other unacceptable hydroxyurea-related non-hematological toxicities, such as mucocutaneous manifestations, gastrointestinal symptoms, pneumonitis, or fever at any dose of hydroxyurea

aAfter three months of at least 2 g/day of hydroxyureabOrgan extending by more than 10 cm from the costal margincComplete response was defined as: hematocrit <45% without phlebotomy, platelet count 400 x109/L, white blood cell count 10 x109/L, and no disease related symptoms. Partial response was defined as: hematocrit <45% without phlebotomy, or response in three or more of the other criteria

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Adapted from: Barosi G, et al. Br J Haematol. 2010;148(6):961-963

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Appendix I

The Canadian MPN group is a non-for profit, charitable national organization whose mission is to improve care and research for patients with MPN through inter-professional collaboration.

For more information about the MPN group and its activities, visit http://mpncanada.com.

Acknowledgements

The authors acknowledge the assistance of Radmila Day and Lori Paluzzi of Fusion MD medical science network, whose help was made possible through funding from Novartis Canada Pharmaceuticals Inc.

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