The mortality outcomes and survival pattern of patients of Myeloproliferative Neoplasms in Malaysia

Background: The prognostication of myeloproliferative neoplasm (MPN) has always been challenging even in the advent of Janus kinase 2 (JAK2 V617F) molecular studies. The survival pattern of MPN in a developing country such as Malaysia is still undetermined. Materials and Methods: This was a retrospective study using information from 774 patients from the National MPN Registry conducted from the year 2009 to 2015 in Malaysia. Patients with the diagnosis of essential thrombocythaemia (ET), polycythaemia vera (PV), primary myelobrosis (PMF) and unclassied MPN (MPN-U) were included. Survival data were traced until December 2018. Results: The cohort consisted of 42.0% ET, 41.0% PV, 8.9% PMF and 8.1% MPN-U, with 48.8% Malay, 39.1% Chinese, 7.1% Indian, 5.0% Others. The subtypes analysis revealed that male MPNs was more than female MPNs except in ET. The Chinese ethnicity was associated with the highest incidence of ET. The mortality rate was the highest in PMF followed by MPN-U then PV and ET (p<0.0001). Survival analysis revealed that the overall survival differed signicantly according to characteristics such as sex, sub-types, JAK2 V617F mutation, bone marrow brosis, presence of splenomegaly, diabetes mellitus, hypertension, and bleeding manifestation. Cox regression analysis identied age, haemoglobin level, sex, and subtype as a signicant risk factor for mortality outcome. Conclusion: Patients with ET had the slightly better OS while PMF had the worst OS. This is in conjunction with low haemoglobin, worsening bone marrow brosis, splenomegaly, diabetes mellitus, hypertension and bleeding. JAK2 V617F mutation was seemingly resulting in inferior overall survival especially in ET and PMF. The survival outcome of the MPN registry is instrumental for future policy development of effective healthcare in Malaysia.


Introduction
Myeloproliferative neoplasm (MPN) has been reclassi ed by the World Health Organization (WHO) in the past few years signifying a paradigm shift in the diagnosis of myeloid neoplasms which includes the subsets like polycythaemia vera (PV), essential thrombocythaemia (ET) and primary myelo brosis (PMF). The reclassi cation is based on clinical characteristics, morphologies, immunophenotyping and genetic studies [1]. The distinction between PV, ET and PMF in terms of prognosis is essential as patients with ET have been shown to have a signi cantly better prognosis than those with PMF and PV, while patients with PMF have the worst survival outcome [1].
The role of Janus Kinase 2 (JAK2 V617F) mutation or its allele burden in prognostication in MPN remains controversial. One retrospective study of 152 patients in the United Kingdom revealed that 83 patients with positive JAK2 V617F mutation were associated with poorer overall survival (OS) [2]. However, another prospective study of 174 patients in Italy stated that the presence of JAK2 V617F mutation was associated with larger spleen size requiring splenectomy and disease progression, to leukaemia transformation but not survival outcomes [3]. Similarly, another study from the United States of America demonstrated that JAK2 V617F had no prognostic signi cance in survival outcome [4]. Similar results are also found in another larger study [5]. There are a number of other adverse prognostic factors identi ed such as old age, marked anaemia, leukocytosis or leukopenia, abnormal karyotypes, presence of constitutional symptoms and presence of circulating blasts [5]. Various vascular complications, including arterial or venous thrombosis and bleeding, might also affect the survival outcomes. There are quite a number of prognostic models derived from mainly clinical and hematologic parameters [6]. The International Prognostic Score for Essential Thrombocythemia (IPSET) which predicts thrombosis based on the major cardiovascular risk factor and JAK2 V617F mutation predicts survival based on age ≥60 years or thrombosis history and presence of JAK2 V617F mutation [6,7]. The PV prognostic model is derived from conventional thrombosis score (European Leukemia Net recommendations) which includes older age, leukocytosis, venous thrombosis, abnormal karyotype and JAK2 V617F allele burden > 50% as adverse risk factors to survival [6,8].
PMF has three prognostic models, namely the International Prognostic Scoring System (IPSS), Dynamic International Prognostic Scoring System (DIPSS) and DIPSS-plus [5,6]. This research is the rst study in Asian countries that reported the survival outcome of patients with MPN with the association to JAK2 V617F mutation, different patients' characteristics and demographics, based on the national registry for MPN. The MPN registry is valuable as it provides an insight into the outcome of MPN in our population in correlation with all the clinical, non-clinical and laboratory parameters.

Materials & Methods
The MPN registry We reported patient demographics such as gender, ethnicity, sub-types, and laboratory ndings including degree of bone marrow (BM) brosis, presence of JAK2 V617F mutation, and presence of splenomegaly. We tabulated the age of diagnosis, mortality rate and mortality age according to patient demographics. Survival analysis was performed to estimate the 5-year and 15-year overall survival (OS) according to patient demographics and presence of diabetes, hypertension and bleeding episodes. Univariable and multivariable Cox regression model was performed to estimate the hazard ratio (HR) of abovementioned characteristics on the survival outcome.
The assumption of proportionality for all categorical variables was assessed using plots of cumulative sums of Martingale residuals and Supremum test. Statistical analyses were performed using R version 3.6.1 at a signi cance level of 5% (2-sided) for all statistical tests.

Survival Outcome
Survival outcome of patients was traced and con rmed with the unique identi cation card (IC) number from the Malaysia National Registration Department up to the end of December 2018. All foreigners were excluded from the analysis as their survival outcome could not be traced without an IC number. The survival duration was calculated from the date of diagnosis until death or end of followup. The cumulative probability of OS was estimated using Kaplan-Meier method and difference in OS between subgroups was tested using the Log-rank test. Multiple comparisons were performed with adjusted signi cance level using the Tukey method. Results were presented in frequency (n) and percentage (%) unless speci ed otherwise.

Results
The age of diagnosis, mortality rate differed signi cantly according to subtypes, as summarized in Table 1 as compared to those without the mutation in ET and PMF in 10 years (p < 0.05). Patients presented with diabetes mellitus in PV, hypertension in ET and bleeding in ET were showing signi cant less favorable outcome compared to those without such manifestations.  (Fig. 1). Male MPN had an inferior OS compared to female (p = 0.0201). Patients with ET and PV had a better OS in comparison to MPN-U and PMF (p < 0.0001). Patients with JAK2 V617F mutation had a worse OS as compared to those without the mutation (p = 0.0310). Patients presented with splenomegaly did worse than those without splenomegaly (p < 0.0001). Survival outcome declined as the BM brosis grade increased from grade 0 to 4 (p < 0.0001). Patients with diabetes mellitus, hypertension and bleeding at presentation had worse OS than those without (p < 0.05), respectively.
The association of characteristics to survival outcome was estimated using a hazard ratio (HR), as summarized in Table 3. Simple Cox regression model identi ed all variables to be signi cant predictors for survival outcomes. For instance, a year increase in age was associated with a 6.3% increase in the risk of dying among MPN patients (p < 0.0001). In the multiple Cox regression model, we identi ed age, HB, sex, and sub-types as signi cant predictors for survival outcome (Fig. 2). Bone marrow brosis grade was excluded from the multiple regression model due to a large amount of missing data. Interestingly, the adjusted HR showed that male faced a higher mortality risk than female (HR = 1.492, p = 0.216). The HR increased from 1.388 in PV, 2.151 in PMF to 2.626 in MPN-U, as compared with ET.

Discussion
The MPN registry was the largest collection speci cally for patients with various sub-types of MPN in Malaysia. The mean mortality age of patients with MPN was 67.5 years, clearly shorter than the expected Malaysia life expectancy, ranged from 72-78 years. Patients who were diagnosed at an older age was associated with an unsatisfactory outcome. A similar result was also demonstrated in many studies. [11][12][13]18]. The possible postulation for these ndings is that elderly patients had likely more aggressive disease and with the presence of other co-morbidities, which resulted in a higher rate of hospitalization and treatment-related complications [11]. According to several myelodysplastic/myeloproliferative neoplasms studies in the United States, ageing is linked to the rising incidence of cancer as a result of immune senescence, autoimmunity, chronic in ammation and accumulating DNA damage [14][15][16].
We found similar gender distribution in our population with the rest of the world [14,17]. The male MPN patients tend to do worse compared to female MPN patients. Female MPN patients tend to do better compared to their counterpart [11,13]. The observed gender disparity possibly due to hormonal effect, occupational exposures, lifestyle factors [14,19,20].
The only peculiar thing that we discovered in our registry was Chinese ethnicity had a higher incidence of ET despite being a much smaller ethnic group compared to Malay. There is a similar nding to the previous paper of epidemiology of this MPN cohort in which Chinese seems to have a relatively higher incidence of death in MPN compared to Malay considering the racial distribution of 21.2% for Chinese and 61.8% for Malay in Malaysia.
[41] Despite the statistical insigni cance, geography and ethnicity are found to in uence the survival in other countries [13]. Maynadie et al. revealed that the survival rates of 74% in Northern Europe in comparison to only 27% survival rates in Eastern Europe [21]. Another study from China also reported the Chinese MPN patients were signi cantly younger, had less splenomegaly or constitutional symptoms with signi cantly better survival when compared with the Caucasian MPN patients [22].
JAK2 V617F mutation was shown to have some in uence on the survival outcome in our patient cohort. This is in contrast to the International Prognostic Scoring System (IPSS) of PMF in which the presence of JAK2 V617F did not in uence the prognosis of PMF [23]. Nevertheless, several studies had demonstrated that there is an association between JAK2 V617F allelic burden with clinical phenotype and disease outcomes in PV patients [24,25]. The suggestion of a possible link between the homozygous allele burden and older age, male gender, pruritus, splenomegaly, thrombosis and MF transformation [24]. Alvarez-Larrán et al. revealed that there was an increased risk of myelo brotic transformation in association with high ( 50%) or unstable JAK2 V617F burden during follow-up and a trend for a higher incidence of thrombosis than patients with allele burden < 50% [26]. Unfortunately, this information was not captured in our study.
Our study demonstrated that PMF had the worst OS in comparison to PV and ET. This is consistent with the ndings from many studies [11,13,27,28]. Low JAK2 V617F allele burden at diagnosis in patients with PMF is associated with shortened survival in PMF [28][29][30]. The inferior OS of PMF in our study can be possibly a result of leukaemic transformation and systemic infections which are documented in the Mayo Clinic study [29] and in the Italian study respectively [30].
The MPN-U was noted to have second-worst overall survival after the PMF. The MPN-U was associated with inferior survival of 12.4 months, compared to 16 months with MDS and 41.5 months with PMF (p < 0.001) in a study by DiNardo et al. [31]. This is further supported by Chaudhury et al. study stating that MDS/MPN-U is associated with poor outcomes in view of a variable disease course [32].
The bone marrow brosis grade 2 to grade 4 was associated with worse overall survival in our study. The accurate evaluation of bone marrow brosis has been highlighted to be a key point to predict prognosis in PMF [33]. Guglielmelli et al. showed that there was a correlation between the higher grades of brosis and survival despite the IPSS variables and mutational status [34]. The median survival was signi cantly reduced in patients with grade 2 and 3 brosis in comparison to grade 1 in a multivariate analysis [34,35].
The bone marrow brosis of grade 2 and above is linked to a more advanced clinical presentation encompassing constitutional symptoms, cytopenias, larger splenomegaly, a higher IPSS risk category and more frequent adverse mutations (ASXL and EZH2) [35].
The patients presented with vasomotor symptoms such as headache, dizziness, tinnitus, syncope, tingling, visual changes, acrocyanosis or erythromelalgia were not signi cantly associated with adverse survival outcome in our study. Twenty-ve per cent (25%) to 35% of patients were asymptomatic, and the thrombocytosis were incidental ndings [36]. The presence of vasomotor symptoms resulted in patients seeking medical attention and treatment early, hence better OS. Whereas, bleeding episodes as an initial ≥ clinical presentation was seemingly linked to worse OS in our study. This was evidenced by the causes of mortality in which the bleeding events were the most frequent reason for death due to underlying disease.
Older age and the presence of diabetes mellitus were the risk factors found to have statistical signi cance for mortality in this study. According to Gangat  The ET patients seemingly had a similar OS in comparison to PV patients within the rst ten years in which conventionally ET is believed to be doing much better compared to other subtypes. The reason maybe there was a possibility of "pre brotic" MF mimicking ET in its presentation. This was probably missed as many patients did not undergo bone marrow biopsy. The revised 2016 WHO classi cation system categorized "pre brotic" MF from "overtly brotic" PMF and it is prognostically relevant to differentiate between the two.
[42] The presence of JAK2 V617F mutation was statistically signi cant for OS in ET and PMF in this study could possibly related to the "pre brotic" MF. There is a number of limitations in this study which includes loss of data, lack of treatment data and inability to determine the cause and effect. The MPN registry included prevalent cases instead of incident cases hence the long survivors would be overrepresented in the registry whereas those who passed away prior to year 2009 would not be included. However, this is the only registry for MPN patients in Malaysia that can provide us with many informative ndings which can be utilized to improve the management of MPN patients in the future.

Conclusion
The presence of JAK2 V617F mutation did show a negative impact on the overall survival of MPN patients in Malaysia especially in ET and PMF. Low haemoglobin, worsening bone marrow brosis with splenomegaly, diabetes mellitus, hypertension and bleeding were associated with reduced overall survival. Patients with ET was found to have slightly better OS, followed by PV while PMF had the worst OS. The MPN-U was associated with inferior outcome after PMF which should be researched further in the future. The survival outcome of these patients is instrumental for future policy development of effective healthcare system in Malaysia.

Declarations
Competing interests: The authors declare no competing interests in this research.

Supplementary Files
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