Patterns of Survival and Causes of Death In 9,384 Patients with Myeloproliferative Neoplasms Diagnosed In Sweden Between 1973 and 2008

Available data on survival patterns among patients diagnosed with myeloproliferative neoplasms (MPN) show a great diversity. For instance, in essential thrombocythemia (ET) there are reports stating that survival is not affected by the disease while other investigators consider ET to be a serious disease that significantly reduces life expectancy. Patients with primary myelofibrosis (PMF) are consistently reported to have a shortened life span while polycythemia vera (PV) is associated with a reduced survival in many, but not all, studies. We conducted a comprehensive, population-based study to assess survival and to define causes of death MPN patients, and to compare patterns to the general population.

The nationwide Swedish Cancer Registry was used to identify all cases of MPN between 1973 and 2008 with follow-up to 2009. Relative survival ratios (RSRs) and excess mortality rate ratios (EMRRs) were computed as measures of survival. The Cause of Death Registry was used to obtain information on causes of death both in the patient and the general population.

A total of 9,384 MPN patients were identified (PV n=4,389, ET n=2,559, PMF n=1,048 and MPN not otherwise specified (MPN NOS) n=1,288); 47% were males and the median age at diagnosis was 71. The reporting rate to the Cancer Registry increased over time being well above 95% during the most recent calendar period.

There was a significant overall excess mortality in all subtypes of MPN, reflected in 5-year and 10-year RSRs of 0.83 (95% CI 0.81–0.84) and 0.64 (0.62-0.67) for PV, 0.80 (0.78-0.82) and 0.68 (0.64-0.71) for ET and 0.39 (0.35-0.43) and 0.21 (0.18-0.25) for PMF, respectively.

Higher age at MPN diagnosis was associated with a poorer survival. For example, the 10-year RSR for patients <50 years was 0.86 (0.83-0.88) as compared to 0.35 (0.29-0.43; p<0.001) in those >80 years. Females had a superior survival, EMRR 0.72 (0.66-0.78), compared to males (reference 1.00).

Survival of patients with MPN improved significantly over time with an EMRR of 0.60 (0.53-0.67) in 1983–1992, 0.29 (0.25-0.34) in 1993–2000 and 0.23 (0.19-0.27) 2001–2008 using the calendar period 1973–1982 as a reference (1.00). However, MPN patients of all subtypes including PV and ET had an inferior survival compared to the general population during all calendar periods indicating that these patients continue to experience higher mortality. The 10-year RSRs for patients diagnosed 1993–2008 were 0.72 (0.67-0.76) for PV and 0.83 (0.79-0.88) for ET (Figure).

The most common causes of death in MPN patients were, in order, hematological malignancy 27.2%, cardiac disease 27.1%, solid tumors 12.4% and vascular events including thromboembolism and bleeding, 9.2%. Four per cent of patients in this cohort were reported to have died due to acute myeloid leukemia. Over time, the proportion of deaths due to cardiac disease and thromboembolic events has decreased. On the other hand, we observed an increasing relative number of deaths due to hematological malignancies during the more recent calendar periods. The relative risks of dying from these causes in relation to the general population will be presented.

In this large population based study including over 9,000 MPN patients, we found all MPN subtypes to have a significantly lower life expectancy compared to the general population. Survival improved over time, however patients of all subtypes including ET had an inferior relative survival even in the most recent calendar period. Especially during earlier years, a certain misclassification and under reporting of ET may have contributed to a reduction in survival rates in the ET group.

The relative number of deaths due to cardiac disease and thromboembolic events decreased during more recent calendar periods. This, and the improvement in survival might reflect the introduction of better treatment strategies for both the disease itself and for the prevention and treatment of thromboembolic complications of MPNs.

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No relevant conflicts of interest to declare.