Rising Incidence and Mortality for Essential Thrombocythaemia

Liam Davenport

May 07, 2021

The incidence of essential thrombocythaemia (ET) has increased steadily in recent years, while that for other myoproliferative neoplasms (MPNs) polycythaemia vera (PV) and primary myelofibrosis (PMF) has remained stable, suggests a large real-world analysis.

The results also indicated that the median overall survival of patients with ET, PV and primary myelofibrosis "was shorter than previously reported," said lead researcher Dr Srdan Verstovsek, PhD, The University of Texas MD Anderson Cancer Center, Houston, USA.

While there was "a trend for improved survival over time in patients with PV and primary myelofibrosis," this was not seen for patients with ET, in whom mortality rates increased.

"Further investigation into the varying survival rates between MPN subtypes is warranted, as findings from this study suggest that improvements in supportive care, strategies or therapies for ET are lagging behind those available for PV and primary myelofibrosis," Dr Verstovsek added.

The research was presented at the British Society for Haematology 2021 Virtual Annual Scientific Meeting on April 26.

Increased Incidental Diagnoses

Approached for comment, Dr Jonathan Cullis, consultant haematologist and Clinical Lead for Cancer Transformation, Salisbury NHS Foundation Trust,  said the results are "interesting" and "quite provocative", although he noted that recent data on MPN incidence pattens showed "similar" results.

He told Medscape News UK that the mortality data on ET was difficult to interpret, other than to suggest it may be due to patients being "diagnosed later in life", which may have "some sort of influence".

The increased diagnostic rates, on the other hand, "probably reflect a number of things," Dr Cullis added, including that "increasingly we pick up haematological cancers on blood tests as an incidental finding".

This is due to the rise in the number of blood tests performed at, for example, well man and well woman clinics and an "increasing tendency to go straight to a test when you go and see your GP."

There is also "greater access to molecular confirmatory tests, and maybe we have a lower threshold for doing those" than 20 years ago, Dr Cullis said.

Another factor is the ageing population, as MPNs "are largely diseases of older people".

Nevertheless, detecting more cases and earlier is "beneficial" in MPN patients, Dr Cullis said, as ET, for example, "does have a risk of thrombotic complications and therefore there is a need to assess the patient’s cardiovascular risk and decide whether they need treatment."

Lack of Recent Data

Presenting the study, Dr Verstovsek explained that MPNs are a group of heterogeneous disorders "driven by recurrent somatic mutations" and, compared with the general population, patients have "reduced overall survival and are at heightened risk for thrombotic events and leukaemic transformation."

Previous studies have suggested that the median overall survival for ET is 19.8 years, while that for PV is 13.5 years, falling to 5.2–5.9 years for patients with primary myelofibrosis.

As the most recent real-world analysis of the incidence and survival of MPNs only covers patients diagnosed up to 2012, the researchers set out to provide a more contemporary analysis, using data from the Surveillance, Epidemiology, and End Results (SEER) Program.

Covering the period from 2002 to 2016, they selected adults diagnosed with ET, PV or primary myelofibrosis using International Classification of Diseases for Oncology histology codes.

Rising Incidence

They included a total of 34,031 patients with MPN, who had a median age of 65–70 years, and 50.5% were female.

The overall incidence rate of ET was 1.55 per 100,000 person-years, rising to 1.73 per 100,000 person-years in women, and 4.65 per 100,000 person-years in people aged 60 years and older.

For PV, the overall incidence rate was 1.57 per 100,000 person-years, which rose to 1.94 per 100,000 person-years in men, and 4.54 per 100,000 person-years in people aged 60 years and older.

In contrast, the overall incidence rate was much lower for primary myelofibrosis, at 0.44 per 100,000 person-years, although it rose to 0.59 per 100,000 person-years in men, and 1.80 per 100,000 person-years in people aged 65 years and older.

Dr Verstovsek reported that, over the study period, the age-adjusted incidence of ET "rose steadily", which was in contrast to PV and primary myelofibrosis, for which the incidence rate "remained relatively stable".

Interestingly, incidence rates were "consistently higher" for all MPN subtypes compared with previous SEER analyses, which he suggested may be due to increased or earlier use of genetic testing to facilitate MPN diagnosis after 2012, or reporting delays to the SEER database.

Diverging Mortality Rates

One, 2- and 5-year mortality rates, estimated using Kaplan-Meier analysis, decreased for PV and primary myelofibrosis over the study period; "a trend that was not observed for patients with ET", Dr Verstovsek said.

Indeed, the 5-year mortality rate for patients with this form of the disease rose from 10.6% in 2002–2006 to 13.8% in 2007–2011, falling back in 2012–2016 to 12.0%.

The median overall survival was the same for ET and PV, at 12.0 years, but was much lower for primary myelofibrosis, at just 3.6 years.

However, overall survival improved over time for primary myelofibrosis patients, rising from 3.3 years in 2002–2006 to 3.6 years in 2007–2011 and 3.8 years in 2012–2016.

There were no significant improvements in overall survival for either ET or PV, although there was a trend towards longer survival in 2012–2016 for patients with PV.

Dr Verstovsek acknowledged that the study was limited by its retrospective nature, and noted that data on mutation status and factors such as treatment patterns, diagnostic criteria, and comorbidities, were not available.

No funding declared.

No relevant financial relationships declared.

BSH 20212 Virtual ASM: Abstract OR-006. Presented 26 April.

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