Wildtype JAK2V617F and normal or high erythropoietin level makes PV very unlikely, and patients should be investigated for secondary causes of polycythemia.Investigations for secondary polycythemia that may be indicated include: i. Chest x-ray ii. Pulse oximetry iii. Arterial blood gas including carboxyhemoglobin and methemoglobin levels iv. Kidney and liver function tests v. Abdominal imaging studies (ultrasound or CT scan) vi. Oxyhemoglobin dissociation curve vii. Sleep studies 7. All patients should be treated with phlebotomy to target hematocrit less than 45%. 8. Low-dose acetylsalicyclic acid (ASA) should be used in all patients without a contraindication.In high-risk PV patients (age 60 years and/or history of thrombosis), cytoreductive therapy should be used with or without phlebotomy in combination with low dose ASA.Conventional cardiovascular risk factors (diabetes, hypertension, hyperlipidemia) should be aggressively managed, and cigarette smoking should be discouraged. 11. Thromboembolic events should be managed according to accepted management guidelines. 12. Thromboprophylaxis should be used after surgery and in other high-risk situations.Polycythemia vera (PV) is a BCR-ABL1-negative myeloproliferative neoplasm (MPN) characterized by erthryocytosis (with increased red cell mass) that is often accompanied by leukocytosis and thrombocytosis. Constitutive JAK-STAT signaling caused by the JAK2V617F mutation within exon 14 is present in ~ 95% of PV patients and by different mutations within exon 12 of the JAK2 gene (4% of PV patients), which are responsible for the pathogenesis of PV 3,4 . The presence of JAK2V617F or a higher allele burden is not directly associated with PV survival or transformation rates 5,6 , however, increased JAK2V617F allele burdens have been associated with fibrotic transformation 7 .# Background
Polycythemia vera (PV) is a clonal stem cell disorder characterized by erythrocytosis, with the majority of cases caused by constitutive activation of the JAK-STAT signal transduction pathway. The disease is associated with burdensome symptoms, reduced quality of life, thrombohemorrhagic complications and potential transformation to myelofibrosis (MF), myelodysplastic syndrome and/or acute myeloid leukemia (AML) 1,2 Guideline Questions 1. What diagnostic and baseline investigations are recommended for adult patients with suspected or confirmed PV? 2. What are the recommended treatment options for PV?

# Search Strategy
This guideline was generated using systematic literature searches of PubMed and MEDLINE databases, ASCO abstracts and proceedings, and ASH abstracts and proceedings. The search included practice guidelines, systematic reviews, meta-analyses, randomized controlled trials and clinical trials. The guidelines were also adapted from the Canadian MPN Group recommendations.

# Target Population
The following guidelines apply to adults over the age of 18 years. Different principles may apply to pediatric patients.

# Recommendations
- Polycythemia vera (PV) should be considered when there is persistent elevation of hemoglobin (>165 g/L in men and >160 g/L in women) or hematocrit (>49% in men and >48% in women).
- JAK2V617F mutation testing and erythropoietin levels should be performed when PV is suspected.
Bone marrow biopsy and aspiration may be necessary in some cases to confirm the diagnosis of PV and to distinguish PV from other myeloproliferative neoplasms.
PV is highly likely when JAK2V617F mutation is present and erythropoietin level is subnormal. When JAK2V617F mutation is seen with normal erythropoietin level, bone marrow biopsy is recommended to differentiate PV from other MPNs. When JAK2V617F is normal and erythropoietin is low, consider JAK2 exon 12 mutational analysis or alternative diagnosis of congenital polycythemia. JAK2 exon 12 testing may be performed via Next Generation Sequencing (NGS) which is currently only available through bone marrow biopsy in Calgary.

# Clinical Manifestations
The estimated incidence of PV is ~ 2.8 per 100,000 among men and ~1.3 per 100,000 in woman with a prevalence of 22 cases per 100,000.
(). The median age of presentation is in the 6 th decade of life with only 1/3 of patients diagnosed younger than 50 years of age 8 .
The symptoms of PV can be variable with a majority of patients diagnosed incidentally by bloodwork.
Splenomegaly is present in 30-40% of patients 9 . Non-specific symptoms such as headache, weakness, dizziness, and excessive sweating are present in 30% to 50% of PV patients and are often related to hyperviscosity resulting from erythrocytosis 10,11 . Fatigue is common and may be related to iron deficiency often found in PV patients at diagnosis, even before the onset of therapeutic phlebotomy.
Specific symptoms such as pruritus, especially after warm baths or showers (aquagenic pruritus) is reported in 70% of patients and suspected to be related to the degranulation of increased mast cells in the skin of PV patients, releasing histamine and other inflammatory mediators 12,13 . Erythromelalgia, described as burning pain in the feet and/or hands accompanied by erythema is seen in up to 28% of patients resulting from microvascular thrombosis and ischemia due to platelet activation and aggregation 14 . Both arterial and venous thrombotic events are a major cause of morbidity and mortality in PV. The incidence of thrombosis is approximately 18 x 1000 person years and accounts for 45% of all PV deaths 9 .

# Diagnostic Evaluation
In the setting of isolated erythrocytosis, it is important to distinguish between primary and secondary polycythemia. Secondary polycythemia is caused by various factors driving erythropoiesis and may include hypoxia-driven mechanisms such as smoking, sleep apnea/hypoventilation, cardiac or pulmonary disease, high altitude or renal artery stenosis. Alternatively, oxygen-independent mechanisms include: drugs (androgens, erythropoietin, tumors-hepatic, renal, hemanigioblastomas) or post renal transplant 2 . Relative polycythemia should also be ruled out and is characterized by an isolated decrease in plasma volume with resultant elevation of hemoglobin, hematocrit and red blood cell count without an increase in red cell mass. Gaisbock's disease, stress erythrocytosis or spurious polycythemia refer to states of chronically low plasma volumes. A careful history and physical exam with select investigations can help distinguish PV from secondary causes (Table 1).   

# Diagnosis
The diagnosis of PV is based on World Health Organization (WHO) criteria utilizing a composite assessment of clinical and laboratory features as shown in Table 3. Recently, 2016 revisions of the WHO classification have been made that have modified diagnostic hemoglobin levels as well as the utility of BM morphology. A bone marrow biopsy is not uniformly required in all cases, in particular, if patients meet previously defined WHO 2008 hemoglobin requirements and there is low likelihood of masked PV. Figure 1 demonstrates an approach to diagnosis with indications for additional molecular testing and bone marrow biopsy. The rationale for the changes is based on recent observations that some JAK2 V617F-positive PV patients present with hemoglobin levels lower than the 2008 WHO threshold with characteristic bone marrow findings of PV. This would be classified as "masked PV" (mPV) and such patients may have increased risk of thrombosis, secondary to late diagnosis and resulting inadequate disease control  . In PV, the classical BM features are increased cellularity with trilineage proliferation (panmyelosis). Megakaryocytes are pleomorphic with varying sizes without significant abnormalities in maturation and minimal reticulin fibrosis (grade1-2) is present 23 .  17 . This was validated in a population-based PV study of 327 patients whereby age >70, leukocyte count >13 x 10 9 /L and thrombosis at time of diagnosis resulted in poorer survival with 10-year survival rates of 84%, 59% or 26% with the presence of none, one or  2risk factors 26 . Overall, 45% of PV-related deaths are associated with cardiovascular disease 27 .
Approximately 10% of PV patients transform into post-polycythemia vera myelofibrosis (PPV-MF), with progressive splenomegaly, MF-related symptoms, and anemia 28 . The IWG criteria for PPV-MF is shown in Table 4. Disease duration (>10 years) and JAK2V617F allele burden (>50%) are associated with a higher risk of evolution to PPV-MF 27,29 . The risk of leukemic transformation has been reported at 2.3% at 10 years and 5.5% at 15 years and remains <10% at 20 years. Older age, abnormal karyotype, and leukocytes 15 X 10 9 /L are independent risk factors for leukemic transformation 30,31 . Post PV AML is an aggressive disease with very poor outcomes. Intensive chemotherapy followed by consolidated by allogeneic transplant is recommended in young fit patients. Hypomethylating agents and/or experimental therapies can be considered 32,33 .  

# Treatment
The main goal of therapy in PV is to prevent thrombohemorrhagic complications and control symptoms. The currently available treatments are non-curative. All patients should be counselled regarding their disease course and associated complications with management of their vascular risk factors. Currently, there are no specific lipid or blood pressure target ranges for individuals with PV. However, with the increased risk of arterial thrombosis, it is important that patients control atherosclerotic risk factors such as hypertension, dyslipidemia, diabetes and obesity as well as smoking cessation. The Framingham Heart Study and the risk assessment tools incorporated in current Canadian Cardiovascular Society guidelines should be applied for general prevention of cardiovascular disease 36 .
The European Leukemia Net (ELN) guidelines for Philadelphia-Negative Classical Myeloproliferative neoplasms (MPNs) recommends that all patients with PV be managed with phlebotomy to maintain a hematocrit (HCT) below 45%, and low-dose Aspirin 35 . Current risk stratification in PV is based on an estimate of thrombosis risk (Table 5) and patients are treated according to their risk group (Figure 2). The ELN has also defined criteria for response which are mainly intended for standardization in clinical trials and are not typically applied as rigorously in clinical practice 37 . 

# Low-risk patients:
Treatment options for low risk patients include phlebotomy and low-dose Aspirin (81 -100 mg/day) 35 (Figure 2)
Phlebotomy.
Phlebotomy is well tolerated and can be performed as an emergency therapy if patients are experiencing symptoms of hyperviscosity as well as an important treatment for long-term maintenance in PV 35,38 . Typically, initial phlebotomy involves removal of 500 mL of blood every other day until a hematocrit of <45% is achieved. Lower quantity (i.e 250 mL) and frequency of phlebotomy should be considered in the elderly or patients with multiple comorbidities such as cardiovascular disease. Once an optimal hematocrit has been obtained a CBC can be assessed every 4-8 weeks and phlebotomy maintenance can be arranged accordingly (i.e every 2-3 months) to maintain Hct levels. Frequent phlebotomies will lead to iron deficiency and eventually result in reactive thrombocytosis and microcytosis. As a result, phlebotomy-induced iron deficiency can lead to complications such as increasing fatigue and restless leg syndrome. Iron supplementation is generally avoided in the setting of PV 9 .
Based on several studies, the recommended HCT target in PV is < 45% 39,40 . The 2013 Italian Cytoreductive Therapy in Polycythemia Vera (CYTO-PV) was a multicenter, randomized controlled trial (n=365) that compared maintaining a HCT of  45% "low hematocrit" to a HCT between 45-50% ("high hematocrit") using phlebotomy and/or hydroxyurea. The primary composite end point was the time until death from cardiovascular causes or major thrombotic events. At a median follow-up of 31 months, the primary end point was 2.7% among those with a HCT of <45% compared to 9.8% in the "high hematocrit" group (HR 3.91; 95% CI, 1.45 to 10.53; P = 0.007). There was no significant between-group difference in the rate of adverse events 40 .
Low-dose Aspirin.
The randomized, placebo-controlled, European Collaboration on Low-Dose Aspirin in Polycythemia Vera (ECLAP) study (n=518) demonstrated a significant risk reduction (RR 0.40) in a combined endpoint of cardiovascular events and venous thrombotic events (nonfatal MI, nonfatal stroke, PE, major venous thrombosis or death from CV causes) with the use of low-dose Aspirin (100 mg daily) over placebo, with no significant increased risk of bleeding 39 . Based on this data, daily low-dose Aspirin is recommended for all PV patients in the absence of contraindications 35 . Low dose Aspirin is effective in alleviating vasomotor microvascular symptoms particularly erythromelagia, which are resulting from platelet-rich arteriolar microthrombi 41 .

# High-risk patients:
High risk patients as shown in Table 5 ( 60 years of age and/or prior history of thrombosis) should be on cytoreductive therapy 35 . Cytoreductive therapy can be considered on an individual case basis (irrespective of risk) in patients with any of the following features 9 : (Figure 2) i. Extreme thrombocytosis (platelet count 150010 9 /L) or if thrombocytosis is associated to bleeding or avWD ii. Progressive leukocytosis 20 -2510 9 /L iii. Symptomatic splenomegaly iv. Severe disease-related symptoms v. Intolerance to phlebotomy

# Cytoreductive therapies.
The European Leukemia Net (ELN) guidelines recommend either hydroxyurea or interferon- as firstline cytoreductive therapy 35 .

# Hydroxyurea.
Hydroxyurea (HU) is an oral antimetabolite that prevents DNA synthesis by inhibiting the enzyme ribonucleoside reductase. Hydroxyurea is typically started at a dose of 15-20mg/kg/day (~1000mg/day). After a response is attained, a maintenance dose is continued to ensure a CBC remains within a normal range with CBC initially performed monthly and every 3 months thereafter once in a steady state 9 . Hydroxyurea is well tolerated with side effects including skin and nail changes, gastrointestinal toxicities, oral and leg ulcers myelosuppression and development of macrocytosis 9 .
In the Polycythemia Vera Study Group (PVSG) trial, patients treated with HU had a lower incidence of thrombosis compared with historical controls treated with phlebotomy (9.8% vs. 32.8%) 42 . Long-term outcomes comparing hydroxyurea to pipobroman were reported in the French Polycythemia Study Group (FPSG) study, which randomly assigned HU versus pipobroman as first-line therapy in 285 patients < 65 years old. Median survivals were 20.3 and 15.4 years for the HU and pipobroman, respectively (P = .008). At 10, 15, and 20 years, cumulative incidence of acute myeloid leukemia/ myelodysplastic syndrome (AML/MDS) was 6.6%, 16.5%, and 24% in the HU arm and 13%, 34%, and 52% in the pipobroman arm (P = .004). Cumulative myelofibrosis incidence at 10, 15, and 20 years was 15%, 24%, and 32% with HU versus 5%, 10%, and 21% with pipobroman (P = .02). This illustrated the higher leukemogenic potential for pipobroman and its lack of suitability as first-line therapy in PV 43 . Hydroxyurea became a preferred first-line agent and although the incidence of evolution to AML with HU has been reported, it has been considered significantly lower than historical controls treated with chlorambucil or radiophosphorus (5.9% vs. 10.6% vs 8.3%, respectively) 42 . Studies have confirmed a low incidence of AML in PV patients treated with hydroxyurea and that exposure to P32, busulphan, and pipobroman (HR, 5.46; 95% CI, 1.84-16.25; P = .0023), but not to hydroxyurea (HU) alone (HR, 0.86; 95% CI, 0.26-2.88; P = .8021), increases the risk for progression to AML/MDS compared with treatment with phlebotomy or interferon 31 . The data for HU use in PV is also extrapolated from essential thrombocythemia (ET) studies. Cortelazzo et al. randomized 114 high-risk ET patients to HU versus no therapy. At a median follow-up of 27 months, 3.6% of patients on HU experienced a thrombotic event compared to 24% of those in the control group 44 . Likewise, in 809 high-risk ET patients, HU plus low dose Aspirin (100mg/day) was compared to Anagrelide plus low dose Aspirin. Hydroxyurea resulted in better reduction of arterial thrombosis, major bleeding and fibrotic progression. Anagrelide resulted in lower venous thrombosis rates however patients on this treatment were more likely to withdraw from their assigned treatment (P<0.001) 45 . The ANAHYDRET study, was a prospective randomized noninferiority phase 3 study of 259 high-risk ET patients. During the total observation time of 730 patient-years, there was no significant difference between the anagrelide and hydroxyurea group regarding incidences of arterial and venous thrombosis, bleeding events, or rates of discontinuation. Disease transformation into myelofibrosis or secondary leukemia was not reported in this study. Anagrelide was considered not inferior compared with hydroxyurea in the prevention of thrombotic complications in patients with ET however, is not considered a first line treatment option in PV 46 .
Although not a common problem in PV, the development of HU resistance or intolerance occurs and has been estimated as 11.5% in a median of 5.8 years from time of diagnosis. Hydroxyurea intolerance/resistance is associated with a 5.6 fold increase risk of death 47 . The ELN panel of experts has developed a standardized definition of resistance and intolerance to HU in PV 34 (Table 6). Younger patients with intolerance/resistance are alternatively treated with Interferon therapy (IFN) or Ruxolitinib. Older patients can be treated with alternatives such as Ruxolitinib or select elderly patients may be considered for busulphan 35 . Any of the following criteria: 1. Need for phlebotomy to keep HCT 400 x 10 9 /L AND WBC >10 x 10 9 /L after 3 months of at least 2 g/day of HU 3. Failure to reduce massive splenomegaly- by more than 50% as measured clinically, OR failure to completely relieve symptoms related to splenomegaly, after 3 months of at least 2 g/day of HU 4. Persistent cytopenias: ANC <1 x 10 9 /L OR plt <100 x 10 9 /L OR Hgb <100 g/l at the lowest dose of HU required to achieve a complete or partial response  5. Presence of leg ulcers or other unacceptable HU-related toxicities, such as mucocutaneous manifestations, GI symptoms, pneumonitis or fever *Spleen more than 10 cm from the costal margin.
Complete response defined as: Hct <45% without phlebotomy, platelet count 400 x 10 9 /L, WBC  10 x 10 9/ Land no disease related symptoms. Partial response defined as: Hct <45% without phlebotomy, or response in three or more of the other criteria 37 .

# Interferon.
Both short-acting Interferon (IFN) and pegylated interferon (IFN)- are effective in controlling blood counts as well as spleen size and symptoms (aquagenic pruritus) in PV, and is considered first-line therapy, particularly in younger patients (< 40 years) 35,48 . Unfortunately, side effects can limit therapy and include autoimmune disorders, flu-like manifestations, depression, heart and ocular disease which have led to permanent discontinuation in 20% to 40% of patients on conventional IFN and 20% to 25% on pegylated IFN 48 . It is contraindicated in patients with mental disorders. IFN is commonly administered subcutaneously at a starting dose of 3 million units daily until a response is achieved. Pegylated IFN is given at a starting dose of 45 g weekly and if there is lack of response after 12 weeks, a dose increase is indicated (90 ug to 135 ug/weekly) The dose should be titrated individually based on efficacy and toxicity with CBC monitoring on a monthly basis.
Apart from the absence of leukemogenic risk, the other benefit of IFN may be its ability to attain molecular responses 48,49 . A phase II study of pegylated interferon alfa-2a (PEG-IFN-alpha-2a) in patients with ET (n=39) and PV (n=40) demonstrated that PEG-IFN-alpha-2a reduces the size of the malignant clones measured by JAK2 allele burden. Overall hematologic response rate was 80% in PV and 81% in ET (complete in 70% and 76% of patients, respectively). Molecular response rates were 38% in ET and 54% in PV, with complete (undetectable JAK2(V617F)) in 6% and 14%, respectively 49 . Two phase III studies comparing HU to pegylated forms of IFN- are ongoing in the United States and Europe; PROUD-PV (NCT01949805) and MPD-RC 112 (NCT01259856), with aims of determining the efficacy of these two therapies as first line cytoreductive agents in high-risk PV and ET.

# Second line therapies:
Ruxolitinib.
Ruxolitinib is a JAK1/JAK2 inhibitor that has demonstrated clinical benefit and has been approved in patients with myelofibrosis 50,51 . A phase II study of PV patients (n=34) who were intolerant or refractory to HU received ruxolitinib for a median of 35 months. Achievement of a HCT <45% without phlebotomy occurred in 97% of patients by week 24. Patients with palpable splenomegaly at baseline, resulted in 44% and 63%, respectively, having a nonpalpable spleen at weeks 24 and 144. The RESPONSE study was a phase III open-label study evaluating the efficacy and safety of ruxolitinib versus investigator determined best available therapy (BAT) in patients with polycythemia vera who were intolerant or refractory to HU. The primary end point was both hematocrit control and  35% reduction in spleen volume at week 32, based on imaging. The primary end point was achieved in 21% of the patients in the ruxolitinib group versus 1% of those in the BAT group (OR 28.64; 95% CI 4.50-1206; P <0.0001). Hematocrit control was achieved in 60% of patients receiving ruxolitinib and 20% of those receiving BAT. Spleen volume reduction occurred in 38% and 1% of ruxolitinib versus BAT patients, respectively. Ruxolitinib achieved  50% reduction in the total symptom score at week 32 in 49% versus 5% of those with BAT. Thromboembolic events occurred in one patient receiving ruxolitinib and in six patients receiving standard therapy however, further investigations are needed to determine its role in reducing thrombotic risk among PV patients 23 . The most common hematologic adverse events (AEs) were anemia and thrombocytopenia; however, no patient in the RESPONSE trial discontinued treatment due to these cytopenias. Common non-hematologic AEs are headache, dizziness, diarrhea, and fatigue and there were herpes zoster infections noted in ~6% of patients.
Ruxolitinib is now approved by Health Canada for treatment of PV patients resistant to or intolerant of a cytoreductive agent.

# Symptom assessment
PV-related symptoms are troublesome to patients, and alleviation of this burden is an important treatment objective. It is important to carefully assess patients' symptoms and to have an objective means to monitor disease progression or response to treatment. The Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score (MPN-SAF TSS) is a validated objective tool for evaluating patient symptoms 11 . The MPN-SAF TSS, also known as MPN10, is a shorter questionnaire that includes 10 items: fatigue, concentration, early satiety, inactivity, night sweats, itching, bone pain, abdominal discomfort, weight loss, and fever. This score has been validated in a prospective study of 1433 patients and results correlated with other measures of disease burden and remains consistent between serial administrations 11 .

# Special Topics

# Pregnancy
Typically, only 10% of PV patients are diagnosed at <40 years of age 52 . PV increases risks for both fetus and mother with less than 60% of pregnancies occurring in PV patients being successful.
Patients are at risk of miscarriages with first trimester losses being most common. Maternal complications include preeclampsia, postpartum hemorrhage and thrombosis 45,53 . Phlebotomy should be used to keep the hematocrit at less than 45% but of note, the physiological changes of pregnancy often can reduce hematocrit levels. Female patients should be advised that HU is contraindicated in pregnancy and, therefore, appropriate contraceptive precautions should be taken while on this therapy and HU should be discontinued in setting of pregnancy. Interferon alfa-2b is recommended for those requiring cytoreductive therapy during pregnancy since all other cytoreductive agents are contraindicated due to possible teratogenic effects. Indications for cytoreduction in pregnancy include if platelet count >1500 x 10 9 /L or related complications of bleeding. There is some evidence that the use of low-dose aspirin throughout pregnancy improves live birth rate. The ELN has published treatment recommendations for PV patients during pregnancy (Table 7). It is recommended that prophylactic low-molecular-weight heparin (LMWH) be used for 6 weeks postpartum in all patients with consideration for its use during pregnancy in high risk pregnancy 9,35 . *Recurrent (3) first-trimester pregnancy loss, intrauterine growth restriction (IUGR), unexplained intrauterine death or if secondary to placental dysfunction, severe preeclampsia necessitation preterm delivery before 34 weeks, significant ante-postpartum hemorrhage, placental abruption, or marked sustained increase of platelets >1500 x 109/L (Adapted from: Gerds A. Oncology 2017;92:179-189 54 ).

# Perioperative Management:
Surgery in patients with PV has a high risk of both peri-operative bleeding and postoperative thromboembolism. In a multicenter retrospective study of 255 PV and ET patients, a high proportion of patients experienced vascular occlusions (7.7%) and major hemorrhage (7.3%) 55 . Elective surgeries should be delayed until cytoreductive measures and/or phlebotomy can be used to achieve blood count control since risks may be lower with hematologic control prior to surgery 56 . It is recommended that hematocrit maintenance <45% and normalization of blood counts be achieved  3 months prior to surgery 57 . Aspirin should be held for 5-7 days before surgery to reduce the risk of hemorrhage. LMWH should be given after surgery to prevent deep venous thrombosis 57 . Mechanical compression stockings are an option for patients with bleeding that prevents the use of anticoagulation. Ruxolitinib has potential rebound effects with discontinuation therefore it is recommended it be continued through surgery. If discontinuations are needed, a taper is required whereby it is discontinued 1-2 weeks prior to surgery 54 . When thromboembolic events do occur, treatment should be according to current management guidelines. Indefinite anticoagulation should be considered because of the high risk of recurrent events.

# Development and Revision History
This guideline was reviewed and endorsed by the Alberta Hematology Tumour Team. Members include . Evidence was selected and reviewed by a working group comprised of members from the Alberta Tumour Teams, external participants identified by the Working Group Lead, and a knowledge management specialist from the Guideline Resource Unit. A detailed description of the methodology followed during the guideline development process can be found in the Guideline Resource Unit Handbook. This guideline was originally developed in 2020.

# Maintenance
A formal review of the guideline will be conducted in 2022. If critical new evidence is brought forward before that time, however, the guideline working group members will revise and update the document accordingly.