Criteria
The 5th edition of the World Health Organization (WHO) classification of haematolymphoid tumours: myeloid and histiocytic/dendritic neoplasms[80]
Major criteria:
Haemoglobin: >165 g/L (>16.5 g/dL) in men; >160 g/L (>16.0 g/dL) in women
or
Haematocrit: >49% in men; >48% in women
Bone marrow biopsy showing hypercellularity for age with trilineage growth (panmyelosis), including prominent erythroid, granulocytic, and megakaryocytic proliferation with pleomorphic, mature megakaryocytes (differences in size)
Presence of Janus kinase 2 (JAK2) V617F or JAK2 exon 12 mutation
Minor criterion:
Subnormal serum erythropoietin level
A diagnosis of PV requires the presence of either all three major criteria, or the first two major criteria plus the minor criterion. Major criterion 2 (bone marrow biopsy) may not be required if there is sustained absolute erythrocytosis (haemoglobin levels >185 g/L [>18.5 g/dL] and >165 g/L [>16.5 g/dL] [haematocrit 55.5% and 49.5%] in men and women, respectively) if major criterion 3 and the minor criterion are present. Initial myelofibrosis (present in up to 20% of patients) can only be detected by performing a bone marrow biopsy; this finding may predict a more rapid progression to overt myelofibrosis (post-PV myelofibrosis).
International Consensus Classification of myeloid neoplasms and acute leukaemias[7]
Major criteria:
Haemoglobin: >165 g/L (>16.5 g/dL) in men; >160 g/L (>16.0 g/dL) in women
or
Haematocrit: >49% in men; >48% in women
or
Increased red blood cell mass (>25% above mean normal predicted value)
Presence of JAK2 V617F or JAK2 exon 12 mutation.
Bone marrow biopsy showing age-adjusted hypercellularity with trilineage proliferation (panmyelosis), including prominent erythroid, granulocytic, and increase in pleomorphic, mature megakaryocytes without atypia.
Minor criterion:
Subnormal serum erythropoietin level.
The diagnosis of PV requires either all 3 major criteria or the first 2 major criteria plus the minor criterion. Major criterion 3 (bone marrow biopsy) may not be required in patients with sustained absolute erythrocytosis (haemoglobin concentrations of >185 g/L [>18.5 g/dL] and >165 g/L [>16.5 g/dL] in women and haematocrit values of >55.5% in men or >49.5% in women) and the presence of a JAK2 V617F or JAK2 exon 12 criteria.
British Committee for Standards in Haematology modified diagnostic criteria for PV[67]
Criteria:
1) JAK2-positive PV (both criteria required for diagnosis)
A1: Persistently raised haematocrit >52% in men, >48% in women, or raised red cell mass (>25% above predicted)
A2: Presence of JAK2 mutation.
2) JAK2-negative PV (diagnosis requires presence of A1-A4 plus another A or two B criteria)
A1: Raised red cell mass (≥25% above predicted) or haematocrit ≥60% in men, ≥56% in women
A2: Absence of JAK2 mutation
A3: No cause of secondary erythrocytosis
A4: Bone marrow histology consistent with PV
A5: Palpable splenomegaly
A6: Presence of acquired genetic abnormality (excluding BCR-ABL1) in haematopoietic cells
B1: Thrombocytosis (platelet count >450 × 10⁹/L [450 × 10³/microlitre or 450,000/microlitre])
B2: Neutrophil leukocytosis (neutrophil count >10 × 10⁹/L [10 × 10³/microlitre or 10,000/microlitre] in non-smokers; >12.5 × 10⁹/L [12.5 × 10³/microlitre or 12,500/microlitre] in smokers)
B3: Radiological evidence of splenomegaly
B4: Low serum erythropoietin.
Conventional risk stratification for PV[67][72][98]
Low risk:
Age <60 years, and
No history of thrombosis.
High risk:
Age ≥60 years, and/or
History of thrombosis.
Mutation-enhanced International Prognostic Scoring System (MIPSS) for PV[84]
The MIPSS-PV is a point-based risk-stratification tool for PV that incorporates the following prognostic factors:
Thrombosis history (1 point)
Leukocyte count ≥15,000/microlitre (15 × 10⁹/L or 15 × 10³/microlitre) (1 point)
Age >67 years (2 points)
Spliceosome mutations (SRSF2) (3 points).
Patients with PV are stratified into the following risk groups based on total points:
Low risk (0-1 points)
Intermediate risk (2-3 points)
High risk (≥4 points).
The European LeukemiaNet (ELN) and International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) response criteria for polycythaemia vera[99]
Complete response is defined as:
Durable (lasting at least 12 weeks) resolution of disease-related signs including palpable hepatosplenomegaly, large symptom improvement (≥10-point decrease in myeloproliferative neoplasm symptom assessment form total symptom score), and[100]
Durable (lasting at least 12 weeks) peripheral blood count remission, defined as haematocrit <45% without phlebotomies, platelet count ≤400,000/microlitre (400 × 10⁹/L or 400 × 10³/microlitre), and white blood cell count <10,000/microlitre (10 × 10⁹/L or 10 × 10³/microlitre), and
Without progressive disease, and absence of any haemorrhagic or thrombotic event, and
Bone marrow histological remission, defined as the presence of age-adjusted normocellularity and disappearance of trilinear hyperplasia, and absence of grade >1 reticulin fibrosis.
Fulfilment of the first three criteria above without bone marrow histological remission, defined as the persistence of trilineage hyperplasia, constitutes a partial remission.
Progression to post-PV myelofibrosis is defined as:[101]
Required criteria:
Additional criteria (two are required):
Anaemia or sustained loss of requirement of either phlebotomy (in the absence of cytoreductive therapy) or cytoreductive treatment for erythrocytosis
A leukoerythroblastic peripheral blood picture
Increasing 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 splenomegaly
Development of ≥1 of 3 constitutional symptoms: >10% weight loss in 6 months, night sweats, unexplained fever [>37.5°C [>99.5°F]).
ELN formal consensus definition of clinical resistance and intolerance to hydroxycarbamide in polycythaemia vera[104]
Need for phlebotomy to keep haematocrit <45% after 3 months of at least 2 g/day of hydroxycarbamide, OR
Uncontrolled myeloproliferation (i.e., platelet count >400 × 10⁹/L or 400 × 10³/microlitre [400,000/microlitre] and WBC count >10 × 10⁹/L or 10 × 10³/microlitre [10,000/microlitre]) after 3 months of at least 2 g/day of hydroxycarbamide, OR
Failure to reduce massive splenomegaly (organ extending >10 cm below the costal margin) by more than 50% as measured by palpation, or failure to completely relieve symptoms related to splenomegaly, after 3 months of at least 2 g/day of hydroxycarbamide, OR
Absolute neutrophil count <1.0 × 10⁹/L or 1.0 × 10³/microlitre [1000/microlitre] or platelet count <100 × 10⁹/L or 100 × 10³/microlitre (100,000/microlitre) or haemoglobin <100 g/L (<10 g/dL) at the lowest dose of hydroxycarbamide required to achieve a complete or partial clinico-haematologic response, OR
Presence of leg ulcers or other unacceptable hydroxycarbamide-related non-haematological toxicities, such as mucocutaneous manifestations, gastrointestinal symptoms, pneumonitis, or fever at any dose of hydroxycarbamide.
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