Epidemiology of Myeloproliferative Neoplasms in Norway
Authors: Roaldsnes Christina , Waage Anders , Nørgaard Mette , Ghanima Waleed 
Published: October 2019

Abstract
Background:
Polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis (MF) are clonal hematological disorders collectively named as myeloproliferative neoplasms (MPN). Discovery of JAK2 mutation in 2005, altered WHO classification for MPN diagnosis in 2008 and availability of new treatment of MPN may have substantial effect on epidemiology of MPN. Published data on epidemiology of MPN after the discovery of JAK2 mutation and the introduction of 2008 WHO classifications for MPN, in particular on the prevalence of MPN, are scarce. We aimed to study the epidemiology of MPN in Norway and to explore the impact of JAK-2 mutation and new guidelines on the incidence of MPN using data from the Norwegian cancer registry.
Method:
We identified 2344 persons diagnosed with MPN from the Norwegian Cancer Registry diagnosed between 1995 and 2012. Registration of cancer in the Norwegian Cancer Registry is mandatory according to the law. We report age-adjusted incidence, prevalence and relative survival of MPN. Age adjusted incidence was reported for 2 years periods from 1995 to 2012. The prevalence was calculated according to the Norwegian population per 31.12.2011.
Results:
A total of 945 cases of PV was identified with a median age at diagnosis of 70 years; 471 males (50%) and 474 females (50%). The overall age-adjusted incidence rate both genders was 0.4/10⁵ in 1995-1997, 0.5/10⁵ in 1998-2000, 0.7/10⁵ in 2001-2003, 0.8/10⁵ in 2004-2007, 2008-2009 and 0.7/10⁵ in 2010-12.
We identified a total of 762 cases of ET with a median age at diagnosis of 65 years, 297 males (39%) and 465 females (61%). The overall age adjusted incidence rate both genders being 0.3/10⁵ in 1995-1997 and 1998-2000, 0.5/10⁵ in 2001-2003 and 2004-2006, 0.9/10⁵ in 2007-2009 and 2010-2012.
A total of 418 cases of MF was identified with a median age at diagnosis of 71 years; 243 males (58%) and 175 females (42%). Age adjusted incidence rates of both genders were 0.2/10⁵ from 1995-2006, 0.3/10⁵ in 2007-2009 and 0.5/10⁵ in 2010-2012. There were a total of 219 persons with unclassified MPN both genders,119 males (54%) and 100 females (46%) and age adjusted incidence rate varied from 0.1-0.2 to 0.1/10⁵ 1995-2012. Per 31.12.2011 the prevalence of PV, ET and MF was 9.2, 8.6 and 3.0 per 10⁵ inhabitants respectively. The survival curves for males and females for the three conditions are shown in the figure.
Conclusions:
This population-based study shows that the incidence of ET and MF almost doubled during the years 2007-2012 as compared to 1995-2006 as shown in the table. This increment in the incidence may possibly be related to improved diagnostics including the JAK2 mutation and the introduction of 2008 WHO-guidelines for MPN. Surprisingly, the discovery of JAK2 does not seem to have had impact on the incidence of PV as indicated by steady incidence rates since 2001. The relative survival was only slightly reduced for PV and ET, but substantially reduced for MF. Only 50% of patients with MF survive for more than 5 years.
Table Incidence of MPN per 105 inhabitants during the period 1995 to 2012 in Norway 1995-97 1998-2000 2001-03 2004-06 2007-09 2010-12 PV 0.4 0.5 0.7 0.8 0.8 0.7 ET 0.3 0.3 0.5 0.5 0.9 0.9 MF 0.2 0.2 0.2 0.2 0.3 0.5
Figure showing the relative survival of PV, ET and MF Figure. showing the relative survival of PV, ET and MF

Disclosures
Roaldsnes: Novartis Norge AS: Research Funding. Ghanima:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.