Thrombotic complications of myeloproliferative neoplasms: risk assessment and risk-guided management

Philadelphia-negative myeloproliferative neoplasms are considered to be acquired thrombophilic states. Thromboses, both arterial and venous (not rarely in unusual sites), are often the initial events leading to the diagnosis. After diagnosis, the yearly incidence of thrombotic events is highly variable, and ranges from approximately 1% to 10%. The identification of patients at risk who may benefit from antithrombotic therapy remains a challenge, and it is currently based on age and history of thrombotic events. However, the predictive value of these clinical characteristics is rather limited. Few prospective studies and even fewer interventional randomized studies are available, and there are no studies designed to formally validate the use of risk stratification. The implementation of laboratory parameters such as leukocytosis and/or the JAK2 V617F mutation into a scoring system may be of interest. The mechanisms at work leading to thrombosis remain largely speculative, but are likely to be complex and multifactorial, with a prominent role of cell-cell interactions, mostly owing to qualitative changes. The long-term treatment options to prevent thrombosis are, schematically, aspirin alone as primary prevention for the low-risk patients, and cytoreduction combined with aspirin for the other patients. In very low-risk young essential thrombocythemia patients, abstention can even be considered. The optimal duration of anticoagulation after a thrombotic event is not established. All antithrombotic therapies should be balanced with the hemorrhagic risk, which can also be increased in these patients.

JAK2-v617F mutation is associated with clinical and laboratory features of myeloproliferative neoplasms

The aim of this study is to investigate the differences of clinical and laboratory parameters between patients with JAK2-V617F positive myeloproliferative neoplasms (MPNs) and JAK2 wild type MPNs. DNA was isolated from peripheral blood granulocytes of 106 patients treated at Rijeka University Hospital Center: 41 with polycythemia vera (PV), 43 with essential thrombocythemia (ET), 9 with primary myelofibrosis (PMF) and 13 with myeloproliferative neoplasm--unclassifiable (MPN-u). The JAK2-V617F mutation was detected using allele specific PCR. Laboratory and clinical parameters were obtained from patient's medical records. The JAK2-V617F mutation was detected in 69% (73/106) patients with MPNs. The results revealed significantly different prevalence of JAK2-V617F mutation, between MPNs entities: 88% in PV 58% in ET, 56% in PMF and 54% in MPNs-unclassified disorders. The JAK2-V617F mutation significantly correlated with higher leukocyte count and alkaline phosphatase co re in ET group and with higher platelets count, leukocyte alkaline phosphatase score and serum lactate dehydrogenase in PV group. Vascular events were associated with elevated platelets count in whole MPNs group, with higher platelets and leukocyte count in ET and with splenomegaly in PVpatients. Clinical and laboratory data revealed significant contribution ofJAK2-V617F mutation to the development of clinical phenotype in patients with distinct subgroups of MPNs.

Polycythemia vera and essential thrombocythemia: 2012 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms primarily characterized by erythrocytosis and thrombocytosis, respectively. Other disease features include leukocytosis, splenomegaly, thrombohemorrhagic complications, vasomotor disturbances, pruritus, and a small risk of disease progression into acute myeloid leukemia or myelofibrosis.

DIAGNOSIS

Almost all patients with PV harbor a JAK2 mutation. When PV is suspected, the presence of a JAK2 mutation confirms the diagnosis and its absence, combined with normal or increased serum erythropoietin level, excludes the diagnosis. Differential diagnosis of ET had to include chronic myelogenous leukemia and prefibrotic myelofibrosis. A JAK2 mutation is found in approximately 60% of patients with ET.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk is defined by the presence of age >60 years or presence of thrombosis history; low-risk is defined by the absence of both of these two risk factors. Presence of extreme thrombocytosis (platelet count >1,000 × 10(9)/L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding. Risk factors for shortened survival in both PV and ET include advanced age, leukocytosis, and history of thrombosis.

RISK-ADAPTED THERAPY

Survival is near-normal in ET and reasonably long in PV. The 10-year risk of leukemic/fibrotic transformation is <1%/1% in ET and <3%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV) and hydroxyurea (high risk PV and ET). Treatment with busulfan or interferon-α is usually effective in hydroxyurea failures. Screening for clinically significant AvWS is recommended before administrating aspirin in the presence of extreme thrombocytosis.

Leukocytosis is a risk factor for recurrent arterial thrombosis in young patients with polycythemia vera and essential thrombocythemia

There is evidence that leukocytosis is associated with an increased risk of first thrombosis in patients with polycythemia vera (PV) and essential thrombocythemia (ET). Whether it is a risk factor for recurrent thrombosis too is currently unknown. In the frame of a multicenter retrospective cohort study, we recruited 253 patients with PV (n = 133) or ET (n = 120), who were selected on the basis of a first arterial (70%) or venous major thrombosis (27.6%) or both (2.4%), and who were not receiving cytoreduction at the time of thrombosis. The probability of recurrent thrombosis associated with the leukocyte count recorded at the time of the first thrombosis was estimated by a receiver operating characteristic analysis and a multivariable Cox proportional hazards regression model. Thrombosis recurred in 78 patients (30.7%); multivariable analysis showed an independent risk of arterial recurrence (hazard ratio [HR] 2.16, 95% CI 1.12-4.18) in patients with a leukocyte count that was >12.4 x 10(9)/L at the time of the first thrombotic episode. The prognostic role for leukocytosis was age-related, as it was only significant in patients that were aged <60 years (HR for arterial recurrence 3.35, 95% CI 1.22-9.19).

Blast phase of essential thrombocythemia: A single center study

Blast phase (BP) may occur as a late event in essential thrombocythemia (ET). This study includes 19 patients with post-ET BP diagnosed and followed in a single institution. At BP, 63% of patients had leukocytosis (white blood cell count >10 x 10(9)/L), 74% had anemia (hemoglobin value <10 g/dL), 74% had thrombocytopenia (platelet count <100 x 10(9)/L), and 84% were over 65 years of age. Cytogenetic analysis was available in 10 patients: six had karyotype aberrations. According to cytogenetic-based risk stratification of de novo acute leukemia (AL), all patients had an unfavorable profile. JAK2 (V617F) mutational status was evaluated in five patients. In two of them, the JAK2 mutation was undetectable in blast cells (one with JAK2-positive ET), whereas in three both granulocytes and blast cells displayed the mutation. Treatment of BP was patient-based according to the performance status and co-morbidities and consisted of palliation in 14 patients, and of induction of remission in five. Median survival was 2.3 months (range 0.2-22.3), irrespective of the treatment received. In conclusion, this study indicates that AL evolved from ET has unfavorable clinical and biological features. JAK2 (V617F)-positive ET may evolve in few instances into JAK2-negative leukemia. The outcome of patients is poor whatever the treatment used.

Essential thrombocythemia: past and present

Essential thrombocythemia (ET) is a clonal myeloproliferative disorder characterized by sustained increase in platelet number and tendency for thromboembolism. A somatic point mutation that causes a constitutive activation of the JAK2 gene is found in one in two ET patients. ET is more common in women, its incidence being 0.6-2.5/100,000 patient/year and the median age at diagnosis is 65-70 years. ET can affect all age groups, including children (0.09 cases/year), and is often diagnosed in the third-fourth decade of life. Rare cases of familial ET have been reported. Miscarriages are 3-4 times more common among women with ET than in the general population, especially in patients carrying JAK2V617F. Microvascular disturbances are typical of ET, but a major thrombosis (2/3 arterial and 1/3 venous; 1, 2-3% patient/year) is the main cause of morbidity and mortality. Age over 60 years and/or previous thrombosis are validated risk factor for thrombosis. Hemorrhages occur in 0.33% patient/year, mainly in those with a platelet count over 1,500 x 10(9)/L. Progression to myelofibrosis and leukemia is more common in patients carrying the JAK2V617F mutation, and is estimated to occur in 0.16% and 0.12% patient/year, respectively. The ET-related mortality ratio with respect to the general population is 1:1, while for polycythemia vera it is 1.6:1. Low-dose aspirin is useful for microvascular disturbances, and in the primary and secondary prevention of major thrombosis in high-risk patients, but it is not recommended in patients with a platelet count over 1,500 x 10(9)/L. Hydroxyurea is used as first-line treatment in high-risk patients. Other drugs available are alpha-interferon, anagrelide, pipobroman and busulphan.

Prevalence of polycythemia vera and essential thrombocythemia

Polycythemia vera (PV) and essential thrombocythemia (ET) are common types of myeloproliferative disorders (MPD), the prevalence of which has not been well documented in the United States. Recent breakthroughs in the molecular etiology of these disorders and the accelerated development of targeted pharmacotherapeutics to treat them underscore the need to define the affected population. In this study, we obtained health claims data from major commercial insurance payers in Connecticut and the Center for Medicare and Medicaid Services to estimate the prevalence of PV and ET. Specifically, logistic regression was utilized to develop algorithms to predict the probability that an individual with claims suggestive of MPD truly has PV or ET, and the algorithms were then applied to health claims to estimate the number of PV and ET patients in Connecticut. As of 2003, the age-standardized prevalence was 22 per 100,000 and 24 per 100,000 for PV and ET, respectively, in Connecticut. Applying the age-specific prevalence of PV and ET to the entire US population resulted in an estimated total of 65,243 patients with PV and 71,078 patients with ET in the United States in 2003. This study is the first to assess the prevalence of PV and ET in a large US population. Given the large number of individuals afflicted with these diseases and the fact that demographic changes alone will further increase the burden of

Essential thrombocythemia in young individuals: frequency and risk factors for vascular events and evolution to myelofibrosis in 126 patients

The frequency of vascular events and evolution to myelofibrosis (MF) in young individuals with essential thrombocythemia (ET) is not well known. The incidence and predisposing factors to such complications was studied in 126 subjects diagnosed with ET at a median age of 31 years (range: 5-40). Overall survival and probability of survival free of thrombosis, bleeding and MF were analyzed by the Kaplan-Meier method and the presence of the Janus Kinase 2 (JAK2) V617F mutation correlated with the appearance of such complications. The JAK2 mutation (present in 43% of patients) was associated with higher hemoglobin (Hb) (P<0.001) and lower platelets at diagnosis. With a median follow-up of 10 years (range: 4-25), 31 thrombotic events were registered (incidence rate: 2.2 thromboses/100 patients/year). When compared with the general population, young ET patients showed a significant increase in stroke (odds ratio 50, 95% CI: 21.5-115) and venous thromboses (odds ratio 5.3, 95% CI: 3.9-10.6). Thrombosis-free survival was 84% at 10 years, with tobacco use being associated with higher risk of thrombosis. Actuarial freedom from evolution to MF was 97% at 10 years. In conclusion, young ET patients have thrombotic events, especially stroke and venous thrombosis, more frequently than generally considered, whereas they rarely transform to MF.

Increased risk of pregnancy complications in patients with essential thrombocythemia carrying the JAK2 (617V>F) mutation

Essential thrombocythemia (ET) may occur in women of childbearing age. To investigate the risk of pregnancy complications, we studied 103 pregnancies that occurred in 62 women with ET. The 2-tailed Fisher exact test showed that pregnancy outcome was independent from that of a previous pregnancy. The rate of live birth was 64%, and 51% of pregnancies were uneventful. Maternal complications occurred in 9%, while fetal complications occurred in 40% of pregnancies. The Mantel-Haenszel method showed that fetal loss in women with ET was 3.4-fold higher (95% confidence interval [CI]: 3-3.9; P < .001) than in the general population. Half of the women studied carried the JAK2 (617V>F) mutation, and a multivariate logistic regression model identified this mutation as an independent predictor of pregnancy complications (P = .01). Neither the platelet count nor the leukocyte count was a risk factor. JAK2 (617V>F)-positive patients had an odds ratio of 2.02 (95% CI: 1.1 - 3.8) of developing complications in comparison with JAK2 (617V>F)-negative patients. Aspirin did not prevent complication in JAK2 (617V>F)-positive patients and appeared to worsen outcome in JAK2 (617V>F)-negative patients. A relationship was found between JAK2 (617V>F) and fetal loss (P = .05). This study indicates that patients carrying the JAK2 (617V>F) mutation have higher risk of developing pregnancy complications.

Incidence of the JAK2 V617F mutation among patients with splanchnic or cerebral venous thrombosis and without overt chronic myeloproliferative disorders

BACKGROUND

Thrombosis of splanchnic or cerebral veins is a typical manifestation of polycythemia vera (PV) or essential thrombocythemia (ET). The recently identified Janus kinase 2 (JAK2) V617F somatic mutation is closely related to chronic myeloproliferative disorders (CMD).

OBJECTIVE

To assess the incidence of the JAK2 V617F mutation among patients with splanchnic or cerebral venous thrombosis with or without overt CMD.

PATIENTS AND METHODS

We searched for the mutation in 139 adult patients (> 18 years old) with thrombosis of hepatic veins (HVT, n = 15), or extrahepatic portal vein (PVT) and/or mesenteric vein (MVT) (n = 79), or cerebral veins (CVT, n = 45). Only 19 patients fulfilled criteria for diagnosis of PV (n = 8) or ET (n = 11) at the time of thrombosis: four had HVT, 11 PVT and/or MVT, and four CVT.

RESULTS

The JAK2 V617F mutation was found in 94.7% [95% CI 75.3-99.0] of the patients with overt CMD at the time of thrombosis, in 21.5% (95% CI 13.8-31.7) of the patients with abdominal venous thrombosis and without overt CMD, and in 4.8% (95% CI 1.3-16.1) of the patients with CVT and without overt CMD. Among the patients without overt CMD or thrombophilia and with unprovoked thrombosis, 29.4% (95% CI 16.8-46.1) with splanchnic venous thrombosis and 42.8% (95% CI 24.4-63.4) with PVT had the JAK2 V617F mutation.

CONCLUSIONS

A substantial proportion of patients with splanchnic venous thrombosis and a small, but significant, number of patients with CVT can be recognized as carriers of the JAK2 V617F mutation in the absence of overt signs of CMD. The clinical significance of such findings deserves further investigation.

Essential thrombocythemia

Essential thrombocythemia (ET) is an acquired myeloproliferative disorder (MPD) characterized by a sustained elevation of platelet number with a tendency for thrombosis and hemorrhage. The prevalence in the general population is approximately 30/100,000. The median age at diagnosis is 65 to 70 years, but the disease may occur at any age. The female to male ratio is about 2:1. The clinical picture is dominated by a predisposition to vascular occlusive events (involving the cerebrovascular, coronary and peripheral circulation) and hemorrhages. Some patients with ET are asymptomatic, others may experience vasomotor (headaches, visual disturbances, lightheadedness, atypical chest pain, distal paresthesias, erythromelalgia), thrombotic, or hemorrhagic disturbances. Arterial and venous thromboses, as well as platelet-mediated transient occlusions of the microcirculation and bleeding, represent the main risks for ET patients. Thromboses of large arteries represent a major cause of mortality associated with ET or can induce severe neurological, cardiac or peripheral artery manifestations. Acute leukemia or myelodysplasia represent only rare and frequently later-onset events. The molecular pathogenesis of ET, which leads to the overproduction of mature blood cells, is similar to that found in other clonal MPDs such as chronic myeloid leukemia, polycythemia vera and myelofibrosis with myeloid metaplasia of the spleen. Polycythemia vera, myelofibrosis with myeloid metaplasia of the spleen and ET are generally associated under the common denomination of Philadelphia (Ph)-negative MPDs. Despite the recent identification of the JAK2 V617F mutation in a subset of patients with Ph-negative MPDs, the detailed pathogenetic mechanism is still a matter of discussion. Therapeutic interventions in ET are limited to decisions concerning the introduction of anti-aggregation therapy and/or starting platelet cytoreduction. The therapeutic value of hydroxycarbamide and aspirin in high risk patients has been supported by controlled studies. Avoiding thromboreduction or opting for anagrelide to postpone the long-term side effects of hydrocarbamide in young or low risk patients represent alternative options. Life expectancy is almost normal and similar to that of a healthy population matched by age and sex.

Essential thrombocythemia/polycythemia vera and pregnancy: the need for an observational study in Europe

The management of pregnant patients with essential thrombocythemia (ET) and polycythemia vera (PV) may be problematic. In the literature there are approximately 300 cases of pregnancies reported in ET and less than 50 pregnancies reported in PV. To reduce the effect of reporting bias, we selected articles with either > 10 pregnancies or at least six patients, and here report on the outcome of 195 pregnancies in ET and 36 pregnancies in PV patients. The live birth rate was approximately 60% in ET and 58% in PV. Spontaneous abortion during the first trimester was the most frequent fetal complication, occurring in 31% of ET pregnancies and in 22% of PV pregnancies, respectively. Major maternal complications were more frequent in PV compared with ET (44.4 versus 7.7%). Treatment with low-dose aspirin during pregnancy in ET seemed to reduce complications and also seemed beneficial during pregnancy in PV. In high-risk pregnancies, the additional use of low molecular weight heparin and/or interferon alpha should be considered. This article also describes a registry for an observational study concerning pregnancy in chronic Philadelphia chromosome-negative myeloproliferative disorders within the European LeukemiaNet. A potential management algorithm for pregnancies in ET or PV is also provided.

Epidemiology of the Myeloproliferative Disorders Polycythemia Vera and Essential Thrombocythemia

The annual incidence of polycythemia vera (PV) and essential thrombocythemia (ET) is approximately 2 and 1.5 per 100,000 inhabitants, respectively, if based on large population surveys and adjusted to a standard population. Survival for ET patients does not differ from that of the general population. However, it appears that PV patients have a significantly higher mortality, at least for patients diagnosed before 1990.

Essential thrombocythemia

Significant progress in our understanding of the molecular pathogenesis of essential thrombocythemia (ET) and the other Philadelphia (Ph) chromosome-negative myeloproliferative disorders (MPDs) has recently been achieved. Unfortunately, the diagnosis of ET still relies on a set of exclusion criteria developed years ago, as recent advances have yet to be evaluated for this purpose. The clinical course of ET is characterized by an increased incidence of thrombotic and hemorrhagic complications and an inherent tendency to progress into myelofibrosis or acute myeloid leukemia (AML). There is concern about undesirable effects of cytoreductive therapy given to prevent vascular events, particularly the risk of accelerating the rate of hematologic transformation. Thus, management involves modification of reversible vascular risk factors and further stratification according to the thrombotic risk. Myelosuppressive agents are not recommended in low-risk patients, whereas controlled studies support the therapeutic value of hydroxyurea (HU) plus aspirin in high-risk cases. Anagrelide or interferon-alpha (IFN-alpha) could be considered as second-line therapy in patients refractory or intolerant of HU. IFN-alpha is preferred in pregnant women.

Mutation of the prothrombin gene and thrombotic events in patients with polycythemia vera or essential thrombocythemia: a cohort study

The association between a prothrombin mutation and the risk of thrombosis was analyzed in 214 patients with polycythemia vera or essential thrombocythemia. The rate for venous thrombotic events was 14.7/100 patient-years in patients with the prothrombin mutation compared to 0.8 in patients without the mutation (rate ratio 17.5).

Pregnancy in essential thrombocythaemia: experience with 40 pregnancies

In this study, the course of 40 pregnancies in 16 women with essential thrombocythaemia (ET) was analysed retrospectively. Of the pregnancies, 45% were complicated, 55% uncomplicated, and 62% resulted in live birth. The most common complication was spontaneous abortion during the first trimester seen in 33% of all pregnancies and comprising 72% of all complications. Two intrauterine foetal deaths occurred at weeks 22 and 28. Three pregnancies were complicated by eclampsia or pre-eclampsia. Nine of 16 women with 29 pregnancies had at least one complicated pregnancy. In seven of 16 women, all 11 pregnancies were uneventful. The non-pregnancy-related symptoms of ET or the platelet count before conception or during pregnancy did not correlate with the risk of pregnancy complications. Treatment with low-dose acetylsalicylic acid (ASA) alone during pregnancy or platelet-lowering drugs before or during pregnancy reduced the risk of complications.

Pathogenesis and management of bleeding in essential thrombocythemia and polycythemia vera

Patients with essential thrombocythemia (ET) and polycythemia vera (PV) have a paradoxical predisposition to bleeding and thrombotic complications that are major causes of morbidity and mortality. Bleeding manifestations are often associated with extreme thrombocytosis that may lead to acquired von Willebrand syndrome (AVWS). Symptomatic AVWS, in this instance, is managed by platelet cytoreductive therapy and, in case of a life-threatening situation, platelet apheresis may be of additional value. Qualitative platelet defects are prevalent in PV and ET but have not been consistently linked to clinical bleeding. However, in vitro and in vivo hemostatic defects in these disorders are either precipitated or exacerbated by the use of aspirin or other nonsteroidal anti-inflammatory drugs. Additional patient management issues are raised during systemic anticoagulation and surgery. This review summarizes putative pathogenetic mechanisms of bleeding and their management in ET and PV.

Essential thrombocythemia

Essential thrombocythemia is a distinct clinical entity within the spectrum of myeloproliferative disorders. There is as yet no pathognomonic diagnostic test, and patients who currently fall into the category of essential thrombocythemia are likely to be heterogeneous. This article discusses diagnostic criteria, clinical features, prognosis, and management.

The rate of progression to polycythemia vera or essential thrombocythemia in patients with erythrocytosis or thrombocytosis

BACKGROUND

The clinical relevance of mild erythrocytosis (hematocrit > 0.48 in women or > 0.51 in men) or thrombocytosis (platelet count > 400 x 10(9) cells/L) in asymptomatic persons is uncertain.

OBJECTIVE

To estimate the frequency of polycythemia vera or essential thrombocythemia in persons with erythrocytosis or thrombocytosis in a general population.

DESIGN

Cohort study.

SETTING

Vicenza, Italy.

PARTICIPANTS

10 000 community dwellers age 18 to 65 years and enrolled in the Vicenza Thrombophilia and Atherosclerosis project.

MEASUREMENTS

Platelet count and hematocrit at baseline in all participants and at second follow-up if baseline results were abnormal. Measurement of erythrocyte sedimentation rate, peripheral arterial saturation, serum erythropoietin level, and leukocyte alkaline phosphatase level; chest radiography; abdominal ultrasonography; and occult fecal blood testing were done in persons with confirmed high hematocrit or platelet counts. Polycythemia vera and essential thrombocythemia were diagnosed according to the Polycythemia Study Group criteria.

RESULTS

At baseline examination, 1 person had polycythemia vera, 1 had essential thrombocythemia, 88 had erythrocytosis, and 99 had thrombocytosis. Second examination confirmed erythrocytosis in 40% (95% CI, 29% to 51%) and thrombocytosis in 8% (CI, 4% to 15%) of those with abnormal baseline results. Among persons with confirmed abnormalities, further evaluation revealed 11 with idiopathic erythrocytosis, 2 with polycythemia vera (3/10 000 [CI, 0.6 to 8.7/10 000]), and 3 with essential thrombocythemia (4/10 000 [CI, 1.09 to 10.2/10 000]). After 5 years of follow-up, 1 additional person with a high platelet count developed essential thrombocythemia, and no persons developed hemorrhagic or thrombotic complications.

CONCLUSIONS

The prevalences of polycythemia vera and essential thrombocythemia were higher than expected in this general population. However, the risks for developing polycythemia vera, essential thrombocythemia, or associated vascular complications in persons with erythrocytosis or thrombocytosis were low.

[Occupational and environmental risk factors for essential thrombocythemia: a case-control study]

BACKGROUND

Essential Thrombocythemia (ET) is a chronic myeloproliferative disorder characterized by a long median survival, even though serious complications such as acute hemorrhagic or thrombotic events are not infrequent. Very few information are available about risk factors for ET because of lack of epidemiological studies focused on this topic.

METHODS

We conducted a case-control study in order to analyze the possible association between ET and some occupational and environmental risk factors. A total of 93 patients enrolled in two hospitals in Turin (Italy) and 280 subjects randomly selected from the general population as controls, were included in the analysis.

RESULTS

We found an association between ET and selected occupations. OR estimates suggest a significant association between ET cooks/waiters (OR 4.96, CI 1.59-16.9) and clerks (OR 2.63, CI 1.53-4.51) and a non significant association between ET and hairdressers (OR 5.10, CI 0.82-31.4), nurses (OR 3.75, CI 0.80-19.4), farmers (OR 1.74, CI 0.84-3.56), electricians (OR 1.42, CI 0.48-3.78), and photographers (OR infinity). Data did not suggest any strong association between environmental risk factors and ET.

CONCLUSIONS

Selected occupations seem to be associated to ET. The association of ET with occupations as hairdressers, farmers and electricians could be attributable to known risk factors for other hematolymphopoietic malignancies such as hair dye, pesticides and magnetic fields. The association with other occupations is more difficult to explain, but all the results we presented are consistent with data from previous studies on onco-hematological diseases.