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Genetic Risk Assessment in Myeloproliferative Neoplasms

      Abstract

      The World Health Organization classification system recognizes 4 variants of JAK2 mutation–enriched myeloproliferative neoplasms (for expansion of gene symbols, use search tool at www.genenames.org): essential thrombocythemia (ET), polycythemia vera (PV), primary myelofibrosis (PMF), and prefibrotic PMF. All 4 disorders are characterized by stem cell–derived clonal myeloproliferation with mutually exclusive driver mutations, including JAK2, CALR, and MPL. The median survival is approximately 20 years for ET, 14 years for PV, and 6 years for PMF; age is the most important determinant of survival with the corresponding median of 33, 24, and 15 years in patients younger than 60 years. Genetic information is the second most important prognostic tool and includes karyotype, driver mutational status, and presence of specific other mutations. Karyotype has been shown to carry prognostic relevance in PV (abnormal vs normal) and PMF (unfavorable vs favorable abnormalities). Driver mutational status is prognostically most relevant in PMF; type 1/type 1-like CALR vs other driver mutational status has been associated with superior survival. In ET, arterial thrombosis risk is higher in patients with JAK2 or MPL mutations whereas MPL-mutated patients might be at risk for accelerated fibrotic progression. ASXL1 and SRSF2 mutations have been associated with inferior overall, leukemia-free, or fibrosis-free survival in both PV and PMF, and a recent targeted sequencing study has identified additional other adverse mutations in both these disorders, as well as in ET. Further enhancement of genetic risk stratification in myeloproliferative neoplasms is possible by combining cytogenetic and mutation information and developing a prognostic model that is adjusted for age.

      Abbreviations and Acronyms:

      ASCT (allogeneic stem cell transplantation), DIPSS (Dynamic International Prognostic Scoring System), ET (essential thrombocythemia), GVHD (graft versus host disease), IPSS (International Prognostic Scoring System), MPN (myeloproliferative neoplasm), PMF (primary myelofibrosis), PV (polycythemia vera), WHO (World Health Organization)
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      Learning Objectives: On completion of this article, you should be able to (1) describe cytogenetic abnormalities in myeloproliferative neoplasms (MPN); (2) list mutations in MPN; and (3) discuss prognostic relevance of cytogenetic abnormalities and mutations in MPN.
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      Myeloproliferative neoplasms (MPN) constitute one of several categories of myeloid neoplasms according to the World Health Organization (WHO) classification system for hematopoietic tumors.
      • Arber D.A.
      • Orazi A.
      • Hasserjian R.
      • et al.
      The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia.
      • Barbui T.
      • Thiele J.
      • Vannucchi A.M.
      • Tefferi A.
      Rationale for revision and proposed changes of the WHO diagnostic criteria for polycythemia vera, essential thrombocythemia and primary myelofibrosis.
      The 2016 WHO MPN category includes chronic myeloid leukemia, which is invariably associated with the BCR-ABL1 mutation (for expansion of gene symbols, use search tool at www.genenames.org); the JAK2 mutation-enriched MPN, which include polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), and prefibrotic PMF; and other less frequent clinic-pathologic entities including chronic neutrophilic leukemia, chronic eosinophilic leukemia—not otherwise specified, and MPN—unclassifiable. The JAK2 mutation–enriched MPN are characterized by stem cell–derived clonal myeloproliferation with mutually exclusive JAK2, CALR, and MPL mutations.
      • Tefferi A.
      Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1.
      • Vannucchi A.M.
      • Rotunno G.
      • Bartalucci N.
      • et al.
      Calreticulin mutation-specific immunostaining in myeloproliferative neoplasms: pathogenetic insight and diagnostic value.
      Polycythemia vera is almost always associated with a JAK2 mutation, primarily the JAK2V617F mutation. JAK2V617F is also the most frequent mutation in ET and PMF, with an incidence of 50% to 70% in both. About 40% of the patients with either ET or PMF harbor CALR (20%-25%), MPL (3%-8%), or none of the 3 driver mutations (ie, are triple negative). Accordingly, the presence, absence, or specific type of driver mutations cannot be used for diagnostic distinction among the different MPN, which is based primarily on bone marrow morphology and peripheral blood counts.
      • Barbui T.
      • Thiele J.
      • Vannucchi A.M.
      • Tefferi A.
      Rationale for revision and proposed changes of the WHO diagnostic criteria for polycythemia vera, essential thrombocythemia and primary myelofibrosis.

      Phenotype

      Phenotypically, PV is defined by clonal erythrocytosis, ET by clonal thrombocytosis, and PMF by characteristic bone marrow morphology. In addition, all 3 disorders might be associated with hepatosplenomegaly (PMF>PV>ET), leukocytosis (PMF>PV>ET), thrombocytosis (ET>PMF>PV), microvascular symptoms (PV>ET>PMF), constitutional symptoms (PMF>PV>ET), thrombohemorrhagic complications (PV>ET>PMF), and variable risk of leukemic transformation (PMF>PV>ET), or fibrotic progression (PV>ET).
      • Tefferi A.
      • Barbui T.
      Polycythemia vera and essential thrombocythemia: 2017 update on diagnosis, risk-stratification, and management.
      Patients with PV or PMF might also experience intractable pruritus, whereas increased rates of first trimester miscarriage have been reported in ET
      • Gangat N.
      • Wolanskyj A.P.
      • Schwager S.
      • Tefferi A.
      Predictors of pregnancy outcome in essential thrombocythemia: a single institution study of 63 pregnancies.
      • Tefferi A.
      Pregnancy and thrombocythemia.
      ; in a recent study, approximately 59% of 292 patients with WHO-defined ET were women and 58% of the study population was younger than 60 years.
      • Tefferi A.
      • Guglielmelli P.
      • Larson D.R.
      • et al.
      Long-term survival and blast transformation in molecularly annotated essential thrombocythemia, polycythemia vera, and myelofibrosis.
      Additional clinical manifestations in PV include symptoms of hyperviscosity and in PMF, progressive anemia, leukoerythroblastosis, extramedullary hematopoiesis, recurrent splenic infarcts, peripheral edema, early satiety, cachexia, and symptoms of portal hypertension, including ascites and variceal bleeding.
      Driver mutations might also influence MPN phenotype.
      • Vannucchi A.M.
      • Rotunno G.
      • Bartalucci N.
      • et al.
      Calreticulin mutation-specific immunostaining in myeloproliferative neoplasms: pathogenetic insight and diagnostic value.
      For example, JAK2V617F-mutated patients with ET or PMF are usually older and display higher hemoglobin and leukocyte counts and lower platelet count.
      • Vannucchi A.M.
      • Antonioli E.
      • Guglielmelli P.
      • Pardanani A.
      • Tefferi A.
      Clinical correlates of JAK2V617F presence or allele burden in myeloproliferative neoplasms: a critical reappraisal.
      JAK2 exon 12–mutated patients with PV are younger and often display predominantly erythroid myeloproliferation. In contrast, CALR-mutated or triple-negative patients with ET are younger and display male preponderance, higher platelet count, and lower hemoglobin and leukocyte counts. CALR-mutated patients with PMF are also younger and present with higher platelet count and lower frequencies of anemia and leukocytosis. The risk of arterial thrombosis in ET is significantly higher in JAK2- or MPL-mutated patients than in CALR-mutated or triple-negative patients; the same might be true in terms of vascular risk in PMF.
      • Finazzi M.C.
      • Carobbio A.
      • Cervantes F.
      • et al.
      CALR mutation, MPL mutation and triple negativity identify patients with the lowest vascular risk in primary myelofibrosis.
      In regard to phenotypic correlates of mutations other than JAK2, CALR, or MPL, the most notable so far has been the impressively significant correlation between U2AF1 mutations and anemia in patients with PMF.
      • Barraco D.
      • Elala Y.C.
      • Lasho T.L.
      • et al.
      Molecular correlates of anemia in primary myelofibrosis: a significant and independent association with U2AF1 mutations.
      • Tefferi A.
      • Finke C.M.
      • Lasho T.L.
      • et al.
      U2AF1 mutations in primary myelofibrosis are strongly associated with anemia and thrombocytopenia despite clustering with JAK2V617F and normal karyotype.

      Clinical Course

      Life expectancy of patients with MPN is worse than that of the sex- and age-matched control population, and the median survival is estimated at 20 years for ET, 14 years for PV, and 6 years for PMF
      • Tefferi A.
      • Guglielmelli P.
      • Larson D.R.
      • et al.
      Long-term survival and blast transformation in molecularly annotated essential thrombocythemia, polycythemia vera, and myelofibrosis.
      ; the corresponding values for patients younger than 60 years were 33, 24, and 15 years. Causes of death include leukemic transformation, with a 15-year estimate of approximately 2.1% to 5.3% for ET, 5.5% to 18.7% for PV, and more than 20% for PMF.
      • Cerquozzi S.
      • Tefferi A.
      Blast transformation and fibrotic progression in polycythemia vera and essential thrombocythemia: a literature review of incidence and risk factors.
      Fibrotic progression rates in ET and PV, during a similar time interval, are estimated at 4% to 11% and 6% to 14%, respectively.
      • Cerquozzi S.
      • Tefferi A.
      Blast transformation and fibrotic progression in polycythemia vera and essential thrombocythemia: a literature review of incidence and risk factors.
      Clinical course in patients with ET or PV might be interrupted by thrombotic and bleeding events in a substantial fraction of the patients, and the particular risk depends primarily on the presence or absence of thrombosis history. In PMF, clinical course is characterized by progressive anemia, symptomatic hepatosplenomegaly, profound constitutional symptoms, and cachexia.

      Mutations

      JAK2 (9p24) mutations are the most prevalent mutations in PV, ET, and PMF, with respective incidences of approximately 99%, 55%, and 65%.
      • Tefferi A.
      Novel mutations and their functional and clinical relevance in myeloproliferative neoplasms: JAK2, MPL, TET2, ASXL1, CBL, IDH and IKZF1.
      • Vannucchi A.M.
      • Antonioli E.
      • Guglielmelli P.
      • Pardanani A.
      • Tefferi A.
      Clinical correlates of JAK2V617F presence or allele burden in myeloproliferative neoplasms: a critical reappraisal.
      • Pardanani A.
      • Lasho T.L.
      • Finke C.
      • Hanson C.A.
      • Tefferi A.
      Prevalence and clinicopathologic correlates of JAK2 exon 12 mutations in JAK2V617F-negative polycythemia vera.
      CALR (19p13.2) mutations are the second most prevalent driver mutations in MPN and are found primarily in ET and PMF, with approximate incidences of 15% to 30%. MPL (1p34) mutations are the least frequent driver mutations in MPN, with approximate incidences of 4% in ET and 8% in PMF. A recent targeted sequencing study revealed that mutations or DNA variants other than JAK2, CALR, or MPL are found in 81% of patients with PMF, 53% with PV, and 53% with ET.
      • Tefferi A.
      • Lasho T.L.
      • Guglielmelli P.
      • et al.
      Targeted deep sequencing in polycythemia vera and essential thrombocythemia.
      • Tefferi A.
      • Lasho T.L.
      • Finke C.M.
      • et al.
      Targeted deep sequencing in primary myelofibrosis.
      The most frequent such mutations in PMF were ASXL1 (36%), TET2 (18%), SRSF2 (18%), and U2AF1 (16%), and 35%, 26%, 10%, and 9% of the patients harbored 1, 2, 3, or 4 or more such variants or mutations, respectively. In PV, the most frequent mutations were TET2 (22%), ASXL1 (12%), and SH2B3 (9%); and in ET, TET2 (16%), ASXL1 (11%), DNMT3A (6%), and SF3B1 (5%); the respective percentages of patients with 1, 2, or 3 or more sequence variants or mutations were 30%, 20%, and 3% for PV and 41%, 8%, and 4% for ET.

      Cytogenetic Abnormalities

      Among the JAK2 mutation–enriched MPN, an abnormal karyotype is most often seen in PMF and least often in ET. In a recent study of 826 informative patients with PMF,
      • Wassie E.
      • Finke C.
      • Gangat N.
      • et al.
      A compendium of cytogenetic abnormalities in myelofibrosis: molecular and phenotypic correlates in 826 patients.
      approximately 43% displayed an abnormal karyotype at the time of their referral; among the group with an abnormal karyotype, 68% consisted of sole aberrations and 14% complex karyotype. The most frequent cytogenetic abnormalities in PMF (and their approximate incidences) were 20q- (23%), 13q- (18%), +8 (11%), +9 (10%), chromosome 1q+ (10%), and −7/7q- (7%). In PV, an abnormal karyotype is seen in approximately 15% of the patients, at the time of their diagnosis, and mostly consists of sole abnormalities. The most frequent cytogenetic abnormalities in PV include –Y, +8, +9, del(20q), and chromosome 1q+.
      • Gangat N.
      • Strand J.
      • Lasho T.L.
      • et al.
      Cytogenetic studies at diagnosis in polycythemia vera: clinical and JAK2V617F allele burden correlates.
      The incidence of an abnormal karyotype is approximately 7% in ET, with +9, chromosome 1q+, and +8 identified as the most frequent abnormalities.
      • Gangat N.
      • Tefferi A.
      • Thanarajasingam G.
      • et al.
      Cytogenetic abnormalities in essential thrombocythemia: prevalence and prognostic significance.

      Genetic Risk Assessment in ET

      Currently established clinical risk factors for survival in ET include advanced age, leukocytosis, and thrombosis.
      • Tefferi A.
      • Rumi E.
      • Finazzi G.
      • et al.
      Survival and prognosis among 1545 patients with contemporary polycythemia vera: an international study.
      • Passamonti F.
      • Thiele J.
      • Girodon F.
      • et al.
      A prognostic model to predict survival in 867 World Health Organization-defined essential thrombocythemia at diagnosis: a study by the International Working Group on Myelofibrosis Research and Treatment.
      In routine clinical practice, some patients with prefibrotic PMF are inaccurately diagnosed and managed as ET. A large international study highlighted the prognostic relevance of distinguishing prefibrotic PMF from true WHO-defined ET, in terms of overall, leukemia-free, and myelofibrosis-free survival, and also identified advanced age, thrombosis history, leukocytosis, and anemia as independent risk factors for overall survival; thrombosis history and extreme thrombocytosis for leukemia-free survival; and advanced age and anemia for fibrotic progression.
      • Barbui T.
      • Thiele J.
      • Passamonti F.
      • et al.
      Survival and disease progression in essential thrombocythemia are significantly influenced by accurate morphologic diagnosis: an international study.
      These findings were confirmed in a subsequent report limited to WHO-defined true ET,
      • Passamonti F.
      • Thiele J.
      • Girodon F.
      • et al.
      A prognostic model to predict survival in 867 World Health Organization-defined essential thrombocythemia at diagnosis: a study by the International Working Group on Myelofibrosis Research and Treatment.
      in which age 60 years and above, leukocyte count 11×109/L or greater, and history of thrombosis were identified as independent risk factors for survival and were also mostly in line with a previous Mayo Clinic study of 605 patients with ET, in which age 60 years and above, leukocyte count 15×109/L or greater, history of thrombosis, anemia below the lower limits of normal, tobacco use, and diabetes were identified as independent risk factors for overall survival and extreme thrombocytosis and anemia below the lower limits of normal for leukemia-free survival.
      • Gangat N.
      • Wolanskyj A.P.
      • McClure R.F.
      • et al.
      Risk stratification for survival and leukemic transformation in essential thrombocythemia: a single institutional study of 605 patients.
      To date, neither overall nor leukemia-free survival has been correlated with karyotype in ET.
      • Gangat N.
      • Tefferi A.
      • Thanarajasingam G.
      • et al.
      Cytogenetic abnormalities in essential thrombocythemia: prevalence and prognostic significance.
      Whether this will change in the future, pending larger studies with an adequate number of informative cases, remains to be seen. As for driver mutational status, prognostic relevance has been found for thrombosis-free (worse in JAK2/MPL-mutated cases) and myelofibrosis-free (worse in MPL-mutated cases) survival but not for overall or leukemia-free survival.
      • Haider M.
      • Elala Y.C.
      • Gangat N.
      • Hanson C.A.
      • Tefferi A.
      MPL mutations and palpable splenomegaly are independent risk factors for fibrotic progression in essential thrombocythemia.
      • Elala Y.C.
      • Lasho T.L.
      • Gangat N.
      • et al.
      Calreticulin variant stratified driver mutational status and prognosis in essential thrombocythemia.
      • Tefferi A.
      • Wassie E.A.
      • Lasho T.L.
      • et al.
      Calreticulin mutations and long-term survival in essential thrombocythemia.
      Interestingly, the presence of JAK2V617F in ET has been associated with a lower risk of fibrotic progression.
      • Barbui T.
      • Thiele J.
      • Passamonti F.
      • et al.
      Survival and disease progression in essential thrombocythemia are significantly influenced by accurate morphologic diagnosis: an international study.
      As mentioned above, a recent targeted sequencing study revealed that 53% of patients with ET carried sequence variants or mutations other than JAK2/CALR/MPL.
      • Tefferi A.
      • Lasho T.L.
      • Guglielmelli P.
      • et al.
      Targeted deep sequencing in polycythemia vera and essential thrombocythemia.
      The particular study identified SH2B3, SF3B1, U2AF1, TP53, IDH2, and EZH2 mutations, at least 1 of which was seen in approximately 15% of the patients, as risk factors for overall, myelofibrosis-free, or leukemia-free survival; the median survival of patients with and without adverse mutations was 9 and 22 years, respectively. Furthermore, the effect on survival of these adverse mutations was not accounted for by current clinically devised prognostic models and the observations were validated in an external cohort of patients. In the particular study, the number of mutations did not provide additional prognostic information.
      Current treatment in ET is directed at prevention of thrombosis and bleeding.
      • Haider M.
      • Gangat N.
      • Lasho T.
      • et al.
      Validation of the revised International Prognostic Score of Thrombosis for Essential Thrombocythemia (IPSET-thrombosis) in 585 Mayo Clinic patients.
      • Haider M.
      • Gangat N.
      • Hanson C.
      • Tefferi A.
      Splenomegaly and thrombosis risk in essential thrombocythemia: the Mayo Clinic experience.
      • Barbui T.
      • Vannucchi A.M.
      • Buxhofer-Ausch V.
      • et al.
      Practice-relevant revision of IPSET-thrombosis based on 1019 patients with WHO-defined essential thrombocythemia.
      In a large international study of WHO-defined ET, 10% to 20% of patients experienced thrombotic complications; thrombosis history, age above 60 years, presence of JAK2V617F, leukocytosis, and cardiovascular risk factors were identified as independent risk factors for arterial thrombosis,
      • Carobbio A.
      • Thiele J.
      • Passamonti F.
      • et al.
      Risk factors for arterial and venous thrombosis in WHO-defined essential thrombocythemia: an international study of 891 patients.
      whereas male sex predicted venous thrombosis. In contrast, a lower risk of thrombosis has been shown in patients with extreme thrombocytosis
      • Carobbio A.
      • Thiele J.
      • Passamonti F.
      • et al.
      Risk factors for arterial and venous thrombosis in WHO-defined essential thrombocythemia: an international study of 891 patients.
      and in those with CALR mutations.
      • Finazzi G.
      • Carobbio A.
      • Guglielmelli P.
      • et al.
      Calreticulin mutation does not modify the IPSET score for predicting the risk of thrombosis among 1150 patients with essential thrombocythemia.
      Mutational landscape and prognostic relevance were recently studied in 359 patients with post-PV or post-ET myelofibrosis.
      • Rotunno G.
      • Pacilli A.
      • Artusi V.
      • et al.
      Epidemiology and clinical relevance of mutations in postpolycythemia vera and postessential thrombocythemia myelofibrosis: A study on 359 patients of the AGIMM group.
      The findings from the particular study included higher JAK2 or CALR mutant allele burden in transformed cases, which did not, however, affect overall survival, and documentation of an adverse survival effect of triple-negative mutational status or SRSF2 mutations on survival of patients with post-ET myelofibrosis. In another similar study,
      • Passamonti F.
      • Mora B.
      • Giorgino T.
      • et al.
      Driver mutations' effect in secondary myelofibrosis: an international multicenter study based on 781 patients.
      the adverse effect of triple-negative status, in terms of blast transformation risk, and type 2/type 2-like CALR variants on overall survival was again found.

      Genetic Risk Assessment in PV

      In the largest international study of more than 1500 patients with PV, independent risk factors for overall survival were advanced age, leukocytosis, venous thrombosis, and abnormal karyotype and for leukemia-free survival advanced age, leukocytosis, and abnormal karyotype.
      • Tefferi A.
      • Rumi E.
      • Finazzi G.
      • et al.
      Survival and prognosis among 1545 patients with contemporary polycythemia vera: an international study.
      The prognostic relevance of karyotype in PV was recently confirmed by a Mayo Clinic study in which univariate analysis identified an abnormal karyotype as adversely affecting overall, leukemia-free, and myelofibrosis-free but not thrombosis-free survival; inferior outcome, as compared with normal karyotype, was also found for unfavorable karyotype, +9, −Y, +8, and del(20q).
      • Cerquozzi S.
      • Barraco D.
      • Hanson C.A.
      • et al.
      Abnormal karyotype and prognosis in polycythemia vera: a single center experience in 239 informative cases.
      The detrimental effect of an abnormal karyotype was independent of other risk factors, including adverse mutations.
      As reiterated before, practically all patients with PV harbor a JAK2 mutation whereas the occurrence of CALR or MPL mutations is rare.
      • Broséus J.
      • Park J.H.
      • Carillo S.
      • Hermouet S.
      • Girodon F.
      Presence of calreticulin mutations in JAK2-negative polycythemia vera.
      • Pardanani A.
      • Lasho T.L.
      • Finke C.M.
      • Tefferi A.
      Infrequent occurrence of MPL exon 10 mutations in polycythemia vera and post-polycythemia vera myelofibrosis.
      Approximately 97% of patients with PV carry the JAK2 exon 14 mutation (ie, JAK2V617F), whereas the remaining 3% carry JAK2 mutations in other exons, including exon 12. Clinical outcome comparisons between JAK2V617F- and JAK2 exon 12–mutated patients have so far not shown significant differences.
      • Passamonti F.
      • Elena C.
      • Schnittger S.
      • et al.
      Molecular and clinical features of the myeloproliferative neoplasm associated with JAK2 exon 12 mutations.
      In contrast, a higher JAK2V617F allele burden has been shown to cluster with fibrotic progression in PV, but it is not clear whether the particular phenomenon represented concordant time-dependent events.
      • Passamonti F.
      • Rumi E.
      • Pietra D.
      • et al.
      A prospective study of 338 patients with polycythemia vera: the impact of JAK2 (V617F) allele burden and leukocytosis on fibrotic or leukemic disease transformation and vascular complications.
      Most recently, a collaborative work between Mayo Clinic and the University of Florence, Italy, found a high prevalence (53%) of mutations or DNA variants, involving 27 genes other than JAK2, CALR, or MPL in patients with PV
      • Tefferi A.
      • Lasho T.L.
      • Guglielmelli P.
      • et al.
      Targeted deep sequencing in polycythemia vera and essential thrombocythemia.
      ; the most frequent mutations included TET2 (22%), ASXL1 (12%), and SH2B3 (9%), and the study identified ASXL1, SRSF2, and IDH2 mutations as “adverse,” affecting overall, leukemia-free, or myelofibrosis-free survival. The prevalence of adverse mutations was 15%, and their prognostic effect was independent of conventional prognostic models; the median survival of patients with and without adverse mutations was 7.7 and 16.9 years, respectively.

      Genetic Risk Assessment in PMF

      Current prognostic models in PMF are mostly based on clinical parameters and include the International Prognostic Scoring System (IPSS),
      • Cervantes F.
      • Dupriez B.
      • Pereira A.
      • et al.
      New prognostic scoring system for primary myelofibrosis based on a study of the International Working Group for Myelofibrosis Research and Treatment.
      applicable at the time of diagnosis, and the Dynamic IPSS (DIPSS),
      • Passamonti F.
      • Cervantes F.
      • Vannucchi A.M.
      • et al.
      A dynamic prognostic model to predict survival in primary myelofibrosis: a study by the IWG-MRT (International Working Group for Myeloproliferative Neoplasms Research and Treatment).
      applicable at any time in the clinical course of the disease. Both IPSS and DIPSS use 5 clinical parameters with independent prognostic contribution: age above 65 years, hemoglobin count less than 10 g/dL, leukocyte count greater than 25×109/L, circulating blasts 1% or more, and presence of constitutional symptoms. Accordingly, 4 risk categories, with median survival ranging from 1.5 years to “not reached,” have been established on the basis of the number of these risk factors.
      Dynamic IPSS was subsequently revised to DIPSS plus, by including red cell transfusion need, platelet count less than 100×109/L, and “unfavorable” karyotype as additional independent risk factors.
      • Gangat N.
      • Caramazza D.
      • Vaidya R.
      • et al.
      DIPSS plus: a refined Dynamic International Prognostic Scoring System for primary myelofibrosis that incorporates prognostic information from karyotype, platelet count, and transfusion status.
      For the purposes of DIPSS plus, unfavorable karyotype included complex karyotype or sole or 2 abnormalities that included +8, −7/7q-, i(17q), inv(3), −5/5q-, 12p-, or 11q23 rearrangement.
      • Hussein K.
      • Pardanani A.D.
      • Van Dyke D.L.
      • Hanson C.A.
      • Tefferi A.
      International Prognostic Scoring System-independent cytogenetic risk categorization in primary myelofibrosis.
      • Caramazza D.
      • Begna K.H.
      • Gangat N.
      • et al.
      Refined cytogenetic-risk categorization for overall and leukemia-free survival in primary myelofibrosis: a single center study of 433 patients.
      Dynamic IPSS plus also has 4 risk categories based on the aforementioned 8 risk factors: low (no risk factors), intermediate 1 (1 risk factor), intermediate 2 (2 or 3 risk factors), and high (≥4 risk factors), with median survival of 15.4, 6.5, 2.9, and 1.3 years, respectively.
      • Gangat N.
      • Caramazza D.
      • Vaidya R.
      • et al.
      DIPSS plus: a refined Dynamic International Prognostic Scoring System for primary myelofibrosis that incorporates prognostic information from karyotype, platelet count, and transfusion status.
      The prognostic importance of karyotype in PMF was further highlighted by exhibiting the extremely poor prognosis associated with a monosomal karyotype or inv(3)/i(17q) abnormalities
      • Tefferi A.
      • Jimma T.
      • Gangat N.
      • et al.
      Predictors of greater than 80% 2-year mortality in primary myelofibrosis: a Mayo Clinic study of 884 karyotypically annotated patients.
      and subsequently by a revised cytogenetic model with 4 cytogenetic risk categories: low (normal karyotype or sole abnormalities of +9, del(13q), or loss of Y chromosome); intermediate 1 (sole abnormalities of del(20q), chromosome 1q duplication, extra sex chromosome, sole translocation); intermediate 2 (sole +8 or other autosomal trisomies, sole 5q-, other sole abnormalities not included in the low or intermediate 1 risk categories, non-monosomal complex karyotype, and ≥2 non–high-risk abnormalities); and high (monosomal karyotype or any set of abnormalities that include inv(3)/i(17q), −7/7q-, 12p-, 11q23)
      • Tefferi A.
      • Wassie E.A.
      • Begna K.
      • et al.
      Revised cytogenetic risk stratification in primary myelofibrosis: a Mayo Clinic study of 903 patients.
      ; the respective median survivals were 4.6, 3.8, 2.6, and 0.9 years.
      Several other DIPSS plus–independent risk factors in PMF have since been reported and included driver mutational status,
      • Tefferi A.
      • Lasho T.L.
      • Tischer A.
      • et al.
      The prognostic advantage of calreticulin mutations in myelofibrosis might be confined to type 1 or type 1-like CALR variants.
      • Tefferi A.
      • Guglielmelli P.
      • Lasho T.L.
      • et al.
      CALR and ASXL1 mutations-based molecular prognostication in primary myelofibrosis: an international study of 570 patients.
      • Tefferi A.
      • Lasho T.L.
      • Finke C.M.
      • et al.
      CALR vs JAK2 vs MPL-mutated or triple-negative myelofibrosis: clinical, cytogenetic and molecular comparisons.
      • Guglielmelli P.
      • Rotunno G.
      • Fanelli T.
      • et al.
      Validation of the differential prognostic impact of type 1/type 1-like versus type 2/type 2-like CALR mutations in myelofibrosis.
      • Guglielmelli P.
      • Lasho T.L.
      • Rotunno G.
      • et al.
      The number of prognostically detrimental mutations and prognosis in primary myelofibrosis: an international study of 797 patients.
      • Guglielmelli P.
      • Biamonte F.
      • Rotunno G.
      • et al.
      COMFORT-II InvestigatorsAssociazione Italiana per la Ricerca sul Cancro Gruppo Italiano Malattie Mieloproliferative (AGIMM) Investigators
      Impact of mutational status on outcomes in myelofibrosis patients treated with ruxolitinib in the COMFORT-II study.
      • Vannucchi A.M.
      • Lasho T.L.
      • Guglielmelli P.
      • et al.
      Mutations and prognosis in primary myelofibrosis.
      presence or absence of mutations other than JAK2, CALR, or MPL,
      • Rotunno G.
      • Pacilli A.
      • Artusi V.
      • et al.
      Epidemiology and clinical relevance of mutations in postpolycythemia vera and postessential thrombocythemia myelofibrosis: A study on 359 patients of the AGIMM group.
      • Passamonti F.
      • Mora B.
      • Giorgino T.
      • et al.
      Driver mutations' effect in secondary myelofibrosis: an international multicenter study based on 781 patients.
      • Tefferi A.
      • Guglielmelli P.
      • Lasho T.L.
      • et al.
      CALR and ASXL1 mutations-based molecular prognostication in primary myelofibrosis: an international study of 570 patients.
      • Guglielmelli P.
      • Lasho T.L.
      • Rotunno G.
      • et al.
      The number of prognostically detrimental mutations and prognosis in primary myelofibrosis: an international study of 797 patients.
      • Vannucchi A.M.
      • Lasho T.L.
      • Guglielmelli P.
      • et al.
      Mutations and prognosis in primary myelofibrosis.
      • Guglielmelli P.
      • Biamonte F.
      • Score J.
      • et al.
      EZH2 mutational status predicts poor survival in myelofibrosis.
      • Tefferi A.
      • Lasho T.L.
      • Abdel-Wahab O.
      • et al.
      IDH1 and IDH2 mutation studies in 1473 patients with chronic-, fibrotic- or blast-phase essential thrombocythemia, polycythemia vera or myelofibrosis.
      such as IDH1/2,
      • Tefferi A.
      • Jimma T.
      • Sulai N.H.
      • et al.
      IDH mutations in primary myelofibrosis predict leukemic transformation and shortened survival: clinical evidence for leukemogenic collaboration with JAK2V617F.
      EZH2,
      • Guglielmelli P.
      • Biamonte F.
      • Score J.
      • et al.
      EZH2 mutational status predicts poor survival in myelofibrosis.
      SRSF2,
      • Lasho T.L.
      • Jimma T.
      • Finke C.M.
      • et al.
      SRSF2 mutations in primary myelofibrosis: significant clustering with IDH mutations and independent association with inferior overall and leukemia-free survival.
      or ASXL1,
      • Vannucchi A.M.
      • Lasho T.L.
      • Guglielmelli P.
      • et al.
      Mutations and prognosis in primary myelofibrosis.
      nullizygosity for JAK2 46/1 haplotype,
      • Tefferi A.
      • Lasho T.L.
      • Patnaik M.M.
      • et al.
      JAK2 germline genetic variation affects disease susceptibility in primary myelofibrosis regardless of V617F mutational status: nullizygosity for the JAK2 46/1 haplotype is associated with inferior survival.
      low JAK2V617F allele burden,
      • Tefferi A.
      • Lasho T.L.
      • Huang J.
      • et al.
      Low JAK2V617F allele burden in primary myelofibrosis, compared to either a higher allele burden or unmutated status, is associated with inferior overall and leukemia-free survival.
      • Guglielmelli P.
      • Barosi G.
      • Specchia G.
      • et al.
      Identification of patients with poorer survival in primary myelofibrosis based on the burden of JAK2V617F mutated allele.
      and increased serum interleukin 8, interleukin 2 receptor, or serum-free light chain levels.
      • Pardanani A.
      • Lasho T.L.
      • Finke C.M.
      • et al.
      Polyclonal immunoglobulin free light chain levels predict survival in myeloid neoplasms.
      • Tefferi A.
      • Vaidya R.
      • Caramazza D.
      • Finke C.
      • Lasho T.
      • Pardanani A.
      Circulating interleukin (IL)-8, IL-2R, IL-12, and IL-15 levels are independently prognostic in primary myelofibrosis: a comprehensive cytokine profiling study.
      In one of the first studies that examined the prognostic relevance of driver and other mutations,
      • Tefferi A.
      • Guglielmelli P.
      • Lasho T.L.
      • et al.
      CALR and ASXL1 mutations-based molecular prognostication in primary myelofibrosis: an international study of 570 patients.
      we reported the longest survival in CALR-mutated patients without ASXL1 mutations (CALR+ASXL1; median survival, 10.4 years), compared with patients with other mutational combinations, including ASXL1-mutated cases without CALR mutations (CALRASXL1+; median survival, 2.3 years). Subsequent studies have clarified the prognostic effect of CALR mutations by distinguishing type 1/type 1-like from type 2/type 2-like CALR variants and by attributing the favorable prognostic effect to type 1/type 1-like CALR variants and showing no prognostic difference between type 2/type 2-like CALR, JAK2, MPL and triple-negative mutational status, although the latter might be associated with a higher risk of leukemic transformation.
      • Tefferi A.
      • Lasho T.L.
      • Tischer A.
      • et al.
      The prognostic advantage of calreticulin mutations in myelofibrosis might be confined to type 1 or type 1-like CALR variants.
      • Guglielmelli P.
      • Rotunno G.
      • Fanelli T.
      • et al.
      Validation of the differential prognostic impact of type 1/type 1-like versus type 2/type 2-like CALR mutations in myelofibrosis.
      Most recently, targeted deep sequencing studies have identified additional adverse mutations in PMF, including CBL, KIT, RUNX1, SH2B3, and CEBPA.
      • Tefferi A.
      • Lasho T.L.
      • Finke C.M.
      • et al.
      Targeted deep sequencing in primary myelofibrosis.
      The presence of any one of these mutations, or ASXL1 or SRSF2 mutations, was shown to have an independent adverse effect on overall (median, 3.6 years vs 8.5 years) or leukemia-free (7-year risk of leukemic transformation estimated at 25% vs 4%) survival.
      • Tefferi A.
      • Lasho T.L.
      • Finke C.M.
      • et al.
      Targeted deep sequencing in primary myelofibrosis.
      The particular study also found the prognostic relevance of the number of adverse mutations, which was in line with an earlier observation
      • Guglielmelli P.
      • Lasho T.L.
      • Rotunno G.
      • et al.
      The number of prognostically detrimental mutations and prognosis in primary myelofibrosis: an international study of 797 patients.
      ; the median survival was 8.5 years in patients with no adverse mutation vs 0.7 years in patients with 3 or more adverse mutations.

      Conclusion

      Drug therapy is currently inadequate to cure their disease or prolong survival of patients with MPN. Allogeneic stem cell transplantation (ASCT) offers the possibility of either cure or durable disease-free remission. Unfortunately, ASCT is associated with a nontrivial risk of treatment-related death or comorbidity, such as graft versus host disease (GVHD) and chronic immunosuppression from drugs used to prevent graft rejection or alleviate GVHD. Because of their relatively longer survival and more indolent clinical course, ASCT is usually not recommended for patients with PV or ET. In PMF and post-ET or post-PV myelofibrosis, ASCT is considered if its associated risk of death or comorbidity can be justified. In other words, it is reasonable to consider ASCT in otherwise transplant-eligible patients whose risk of premature death or leukemic transformation is unacceptably high for the individual patient, primarily considering their age. Such therapeutic decision making requires a comprehensive assessment of clinical and genetic risk factors, which are also taken into account when deciding on clinical trial participation. The risk-benefit balancing act is also dependent on ongoing advances being made in the prevention and treatment of GVHD and in reducing the risk of post-ASCT relapse possibly through preemptive treatment. It is our opinion that genetic information not only is helpful in predicting survival outcome or risk of disease complications but also can be applied for monitoring treatment response as well as assessing risk of relapse after drug therapy or ASCT. To that end, it is imperative that clinical trials include laboratory correlative studies that are genetically pertinent.

      Supplemental Online Material

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