Polycythemia vera | |
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Other names | Polycythaemia vera (PV, PCV), erythremia, primary polycythemia, Vaquez disease, Osler-Vaquez disease, polycythemia rubra vera [1] |
Blood smear from a patient with polycythemia vera | |
Specialty | Oncology, hematology |
In oncology, polycythemia vera (PV) is an uncommon myeloproliferative neoplasm in which the bone marrow makes too many red blood cells. [1] The majority of cases [2] are caused by mutations in the JAK2 gene, most commonly resulting in a single amino acid change in its protein product from valine to phenylalanine at position 617. [3]
Most of the health concerns associated with polycythemia vera are caused by the blood being thicker as a result of the increased red blood cells. It is more common in the elderly and may be symptomatic or asymptomatic. Common signs and symptoms include itching (pruritus), and severe burning pain in the hands or feet that is usually accompanied by a reddish or bluish coloration of the skin. Patients with polycythemia vera are more likely to have gouty arthritis. Treatment consists primarily of phlebotomy as well as oral chemotherapy and emerging treatments like long-acting interferon formulations.
People with polycythemia vera can be asymptomatic. [4] Clinical symptoms of polycythemia vera are mostly due to hyperviscosity of blood. A classic symptom of polycythemia vera is pruritus or itching, particularly after exposure to warm water (such as when taking a bath), [5] which may be due to abnormal histamine release [6] [7] or prostaglandin production. [8] Such itching is present in approximately 40% of patients with polycythemia vera. [9] Gouty arthritis may be present in up to 20% of patients. [9] Peptic ulcer disease is also common in patients with polycythemia vera; most likely due to increased histamine from mast cells, but may be related to an increased susceptibility to infection with the ulcer-causing bacterium H. pylori . [10]
A classic symptom of polycythemia vera (and the related myeloproliferative disease essential thrombocythemia) is erythromelalgia. [11] This is a burning pain in the hands or feet, usually accompanied by a reddish or bluish coloration of the skin. Erythromelalgia is caused by an increased platelet count or increased platelet "stickiness" (aggregation), resulting in the formation of tiny blood clots in the vessels of the extremity; it responds rapidly to treatment with aspirin. [12] [13] Splenomegaly may cause the spleen to be palpable in some patients, which has been reported by Lee et al. (2022) to be associated with both the V617F mutation and the development of myelofibrosis. [14]
Polycythemia vera (PV), being a primary polycythemia (increase in the fraction of volume occupied by red cells in the blood), is caused by neoplastic proliferation and maturation of erythroid, megakaryocytic and granulocytic elements to produce what is referred to as panmyelosis. In contrast to secondary polycythemias, PV is associated with a low serum level of the hormone erythropoietin (EPO). Instead, PV cells often carry activating mutation in a tyrosine kinase–encoding gene, JAK2 , which acts in signaling pathways of the EPO receptor, making those cells proliferate independently from EPO. [15] [ page needed ]
Diagnostic criteria for polycythemia vera were modified by the World Health Organization in 2016. [16] The WHO criteria for polycythemia vera are specifically outlined in Table 4, and emphasis is given to accurate histological observations as proven predictors in the prognosis of the disease.
As summarized by Verstovek following the 2016 European Hematology Association Congress, [17] there are 3 major criteria for PV diagnosis:
Patients usually have a very low level of erythropoietin, a growth factor that increases the production of red blood cells, which may be considered a minor diagnostic feature.
A mutation in the JAK2 kinase (V617F) is strongly associated with polycythemia vera. [18] [19] While it is a JAK2 V617F mutation in 95% of patients, JAK2 exon 12 mutations have also been observed. [20] The V617F mutation is not inherited, but develops as a somatic mutation in the erythroid progenitor cells. [21] Some patients may lose the normal allele in the diseased cells entirely together with the short arm of chromosome 9 (9p), likely due to mitotic recombination causing copy-neutral loss of heterozygosity. [22] While the JAK2 V617F mutation is generally sporadic (random), a certain inherited haplotype of JAK2 has been associated with its development. [23] [24]
People with untreated polycythemia vera have a substantial risk of Budd-Chiari syndrome (hepatic vein thrombosis). [25]
Untreated, polycythemia vera can be fatal, with the median survival in patients being 1.5-3 years. [26] [27] [28] Data on the effect of life-span of an individual with treated polycythemia vera is inconclusive due to the rarity of the disease. Studies show the median survival rate of controlled Polycythemia Vera ranges from 10 to 20 years; however, most observations are of people diagnosed in their 60s. Patients live close to a normal life expectancy. [29]
Frequent blood withdrawals (phlebotomy) are one form of treatment, which often may be combined with other therapies. The removal of blood from the body induces iron deficiency, thereby decreasing the hemoglobin / hematocrit level, and reducing the risk of blood clots. Phlebotomy is typically performed to bring their hematocrit (red blood cell percentage) down below 45 for men or 42 for women. [30] It has been observed that phlebotomy also reduces cognitive impairment. [31]
Medications are also used which reduce the number of red blood cells. These include hydroxyurea and interferon therapy, among others. [32] The tendency of some practitioners to avoid chemotherapy if possible, especially in young patients, is a result of research indicating possible increased risk of transformation to acute myelogenous leukemia (AML). While hydroxyurea is considered a safer chemotherapy in this aspect, there is still some debate about its long-term safety. [33]
There are indications that the lung cancer drug erlotinib may be an additional treatment option for those with certain genetic markers. [34]
Ruxolitinib (brand name Jakafi), a Janus kinase 2 (JAK2) inhibitor, is also used to treat polycythemia. [35]
Ropeginterferon alfa-2b (Besremi) was approved for medical use in the European Union in February 2019, [36] and in the United States in November 2021. [37] [38] Ropeginterferon alfa-2b is the first medication approved by the U.S. Food and Drug Administration (FDA) to treat polycythemia vera that people can take regardless of their treatment history, and the first interferon therapy specifically approved for polycythemia vera. [37] Interferon alfa-2b is also used. [32]
Polycythemia vera occurs in all age groups, [39] although the incidence increases with age. One study found the median age at diagnosis to be 60 years, [9] while a Mayo Clinic study in Olmsted County, Minnesota found that the highest incidence was in people aged 70–79 years. [40] The overall incidence in the Minnesota population was 1.9 per 100,000 person-years, and the disease was more common in men than women. [40] A cluster around a toxic site was confirmed in northeast Pennsylvania in 2008. [41]
Janus kinase (JAK) is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. They were initially named "just another kinase" 1 and 2, but were ultimately published as "Janus kinase". The name is taken from the two-faced Roman god of beginnings, endings and duality, Janus, because the JAKs possess two near-identical phosphate-transferring domains. One domain exhibits the kinase activity, while the other negatively regulates the kinase activity of the first.
Polycythemia is a laboratory finding in which the hematocrit and/or hemoglobin concentration are increased in the blood. Polycythemia is sometimes called erythrocytosis, and there is significant overlap in the two findings, but the terms are not the same: polycythemia describes any increase in hematocrit and/or hemoglobin, while erythrocytosis describes an increase specifically in the number of red blood cells in the blood.
The Philadelphia chromosome or Philadelphia translocation (Ph) is a specific genetic abnormality in chromosome 22 of leukemia cancer cells. This chromosome is defective and unusually short because of reciprocal translocation, t(9;22)(q34;q11), of genetic material between chromosome 9 and chromosome 22, and contains a fusion gene called BCR-ABL1. This gene is the ABL1 gene of chromosome 9 juxtaposed onto the breakpoint cluster region BCR gene of chromosome 22, coding for a hybrid protein: a tyrosine kinase signaling protein that is "always on", causing the cell to divide uncontrollably by interrupting the stability of the genome and impairing various signaling pathways governing the cell cycle.
Chronic myelogenous leukemia (CML), also known as chronic myeloid leukemia, is a cancer of the white blood cells. It is a form of leukemia characterized by the increased and unregulated growth of myeloid cells in the bone marrow and the accumulation of these cells in the blood. CML is a clonal bone marrow stem cell disorder in which a proliferation of mature granulocytes and their precursors is found; characteristic increase in basophils is clinically relevant. It is a type of myeloproliferative neoplasm associated with a characteristic chromosomal translocation called the Philadelphia chromosome.
In hematology, essential thrombocythemia (ET) is a rare chronic blood cancer characterised by the overproduction of platelets (thrombocytes) by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid leukemia or myelofibrosis. It is one of the blood cancers wherein the bone marrow produces too many white or red blood cells, or platelets.
Hypereosinophilic syndrome is a disease characterized by a persistently elevated eosinophil count in the blood for at least six months without any recognizable cause, with involvement of either the heart, nervous system, or bone marrow.
Primary myelofibrosis (PMF) is a rare bone marrow blood cancer. It is classified by the World Health Organization (WHO) as a type of myeloproliferative neoplasm, a group of cancers in which there is activation and growth of mutated cells in the bone marrow. This is most often associated with a somatic mutation in the JAK2, CALR, or MPL genes. In PMF, the bony aspects of bone marrow are remodeled in a process called osteosclerosis; in addition, fibroblasts secrete collagen and reticulin proteins that are collectively referred to as fibrosis. These two pathological processes compromise the normal function of bone marrow resulting in decreased production of blood cells such as erythrocytes, granulocytes and megakaryocytes, the latter cells responsible for the production of platelets.
Myeloproliferative neoplasms (MPNs) are a group of rare blood cancers in which excess red blood cells, white blood cells or platelets are produced in the bone marrow. Myelo refers to the bone marrow, proliferative describes the rapid growth of blood cells and neoplasm describes that growth as abnormal and uncontrolled.
Signal transducer and activator of transcription 5 (STAT5) refers to two highly related proteins, STAT5A and STAT5B, which are part of the seven-membered STAT family of proteins. Though STAT5A and STAT5B are encoded by separate genes, the proteins are 90% identical at the amino acid level. STAT5 proteins are involved in cytosolic signalling and in mediating the expression of specific genes. Aberrant STAT5 activity has been shown to be closely connected to a wide range of human cancers, and silencing this aberrant activity is an area of active research in medicinal chemistry.
Janus kinase 2 is a non-receptor tyrosine kinase. It is a member of the Janus kinase family and has been implicated in signaling by members of the type II cytokine receptor family, the GM-CSF receptor family, the gp130 receptor family, and the single chain receptors.
ETV6 protein is a transcription factor that in humans is encoded by the ETV6 gene. The ETV6 protein regulates the development and growth of diverse cell types, particularly those of hematological tissues. However, its gene, ETV6 frequently suffers various mutations that lead to an array of potentially lethal cancers, i.e., ETV6 is a clinically significant proto-oncogene in that it can fuse with other genes to drive the development and/or progression of certain cancers. However, ETV6 is also an anti-oncogene or tumor suppressor gene in that mutations in it that encode for a truncated and therefore inactive protein are also associated with certain types of cancers.
The thrombopoietin receptor also known as the myeloproliferative leukemia protein or CD110 is a protein that in humans is encoded by the MPL oncogene.
CD177 antigen is a protein that in humans is encoded by the CD177 gene.
Basophilia is the condition of having greater than 200 basophils/μL in the venous blood. Basophils are the least numerous of the myelogenous cells, and it is rare for their numbers to be abnormally high without changes to other blood components. Rather, basophilia is most often coupled with other white blood cell conditions such as eosinophilia, high levels of eosinophils in the blood. Basophils are easily identifiable by a blue coloration of the granules within each cell, marking them as granulocytes, in addition to segmented nuclei.
Lestaurtinib is a tyrosine kinase inhibitor structurally related to staurosporine. This semisynthetic derivative of the indolocarbazole K252a was investigated by Cephalon as a treatment for various types of cancer. It is an inhibitor of the kinases fms-like tyrosine kinase 3 (FLT3), Janus kinase 2 (JAK2), tropomyosin receptor kinase (trk) A (TrkA), TrkB and TrkC.
Givinostat, sold under the brand name Duvyzat is a medication used for the treatment of Duchenne muscular dystrophy. It is a histone deacetylase inhibitor with potential anti-inflammatory, anti-angiogenic, and antineoplastic activities. It is a histone deacetylase (HDAC) inhibitor that works by targeting pathogenic processes to reduce inflammation and loss of muscle.
Ruxolitinib is a medication used for the treatment of intermediate or high-risk myelofibrosis, a type of myeloproliferative neoplasm that affects the bone marrow; polycythemia vera, when there has been an inadequate response to or intolerance of hydroxyurea; and steroid-refractory acute graft-versus-host disease. Ruxolitinib is a Janus kinase inhibitor. It was developed and marketed by Incyte Corp in the US under the brand name Jakafi, and by Novartis elsewhere in the world, under the brand name Jakavi.
Fedratinib, sold under the brand name Inrebic, is an anti-cancer medication used to treat myeloproliferative diseases including myelofibrosis. It is used in the form of fedratinib hydrochloride capsules that are taken by mouth. It is a semi-selective inhibitor of Janus kinase 2 (JAK-2). It was approved by the FDA on 16 August 2019.
Clonal hypereosinophilia, also termed primary hypereosinophilia or clonal eosinophilia, is a grouping of hematological disorders all of which are characterized by the development and growth of a pre-malignant or malignant population of eosinophils, a type of white blood cell that occupies the bone marrow, blood, and other tissues. This population consists of a clone of eosinophils, i.e. a group of genetically identical eosinophils derived from a sufficiently mutated ancestor cell.
CHZ868 is a drug which acts as a Janus kinase inhibitor selective for the JAK2 subtype. It was one of the first Janus kinase inhibitors developed, originally for the treatment of leukemia and related blood cancers, and while it did not get approved for clinical use, it is still used for research in the area.