Theoriginaldescriptionsof CALR mutationsinmyeloproliferative neoplasms(MPN)suggestedasignificantimpactondiseasephenotype andoutcome.2,3In1ofthese2seminalreports,2CALR-mutatedpatients with ET, compared with their JAK2-mutated counterparts, displayed higherplateletcount,lowerleukocytecount,lowerhemoglobinlevel, lowerriskofthrombosis,andbettersurvival.Theauthorsalsoreported higher platelet count, lower leukocyte count, and better survival in CALR-mutatedPMFpatients,comparedwithJAK2-mutatedcases.2In the second study,3 CALR-mutated ET patients were associated with higherplateletcount,lowerhemoglobinlevel,andhigherincidenceof fibrotic transformation, compared with JAK2-mutated cases.3 Subsequent reports did not find significant difference in survival orriskof fibrotictransformationbetweenCALR-andJAK2-mutated ET.4,5,7 InPMF,thefavorableimpactofCALRmutationsonsurvival2 wasconfirmedinasubsequentstudy,6 whichalsodisclosedtheprognosticallydetrimentaleffect of “triple-negative” mutationalstatus(ie, wildtypeforJAK2,CALRandMPL).Thelatterstudy6andsubsequent reports10,11 showed further prognostic modifications by ASXL1 mutational status and number of prognostically detrimental mutations. Mutant CALR vs JAK2 mutations in PMF were also associated with younger age, lower hemoglobin level, lower risk disease, and lower frequency of spliceosome mutations.6 More recent reports have suggesteddifferentialphenotypicandprognosticeffectsfromdistinctmutant CALRvariants,includinganassociationoftype2vstype1variants with higher platelet count in ET12 and worse prognosis in PMF.13 JAK2 mutations in ET are often accompanied by distinct biological and clinical characteristics,1 suggesting the possibility of a JAK2 mutation-associated disease continuum that is phenotypically patternedby additionalgenetic or biologicchanges. Consistent withthis concept,somehavearguedthatPVandJAK2-mutatedETaredifferent phasesofthesamediseaseandsharesimilarnaturalhistory,including survival.5,14Thecurrentstudyaddressesthisissuebycomparinglongtermsurvivalandblasttransformation(BT)ratesbetweenPV,ET,and PMF, in the context of their specific JAK2/MPL/CALR mutational status; we also examined the impact of JAK2/MPL/CALR mutational status on long-term disease outcome in ET and PMF.MethodsThe current study was approved by the institutional review boards of Mayo Clinic (Rochester, MN), University of Florence (Florence, Italy), and Papa GiovanniXXIIIHospital(Bergamo,Italy)andconductedinaccordancewith the Declaration of Helsinki. To obtain mature survival data, study eligibility criteria included a diagnosis date prior to 2006 for ET and PV and 2011 for PMF. In addition, for ET and PMF, only those patients whose mutational status, in terms of JAK2, CALR, orMPL, was known were included in the current study. The performance of mutation screening was solely based on
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