Researchers found that in patients with secondary myelofibrosis (SMF), the annual incidence of thrombotic events (TEs) was 2.3% of patients per year. They also reported that in their study they saw a reduction in TE risk with the use of cytoreductive therapy at the time of SMF evolution. The researchers reported the study’s findings in the journal Leukemia.

The researchers evaluated data from 1258 patients with SMF included in the MYelofibrosis SECondary to PV and ET Collaboration (MYSEC) project dataset to characterize patterns associated with TEs in patients with SMF. The aims of the study were to measure the incidence of TEs with SMF, in addition to predictors of TEs that had previously been unidentified.

The researchers included 1258 patients with SMF from the MYSEC cohort in their analyses. Patients across the cohort had a median age of 64 years (range 20-95) and a median duration of polycythemia vera or essential thrombocythemia of 11.2 years (range, 1-41.4). The median study follow-up was 3.5 years (range, 1-21.4), and 10.7% of the patients experienced a first TE during the time since SMF evolution.

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The annual incidence of TEs was 2.3% (95% CI, 1.9%-2.7%) of patients per year across all patients with SMF. Among TEs with information available on vascular site, venous TEs were more common than arterial TEs were overall, with venous TEs representing 67.2% of TEs occurring post-SMF evolution. For venous TEs, the incidence was 1.4% (95% CI, 1.1%-1.7%) of patients per year, while for arterial TEs the incidence was 0.77% (95% CI, 0.6%-1.0%) of patients per year.

The use of cytoreductive therapy during the time of evolution of SMF was linked to an absolute risk reduction of TEs estimated to be 3.3% within 3 years, in a competing-risk analysis. Conventional cytoreductive therapy showed a significant reduction in TE risk, with a hazard ratio (HR) of 0.41 (95% CI, 0.26-0.65; P =.0001). With JAK-inhibitor therapy, the HR for TE risk reduction was 0.50 (95% CI, 0.24-1.02; P =.05).

Multivariable analysis revealed the use of cytoreductive therapy at baseline to be an independent factor in predicting TE risk across vascular sites after SMF evolution had occurred (HR, 0.46; 95% CI, 0.26-0.83; P =.0009). A hemoglobin level of below 11 g/dL was also an independent predictor of TE risk in this analysis (HR, 1.70; 95% CI, 1.02-2.82; P =.04).

The researchers also reported that fatalities had occurred with approximately half (48%) of the patients in the cohort. There were fatal TEs reported in 2.4% of patients in the study.

“In conclusion, within a cohort of 1258 patients affected by SMF, 10.7% reported a first thrombotic complication, corresponding to an annual incidence of 2.3% patients per year. Venous events represented two-thirds of the total,” the researchers wrote in their report.


Mora B, Gugliemelli P, Kuykendall A, et al. Prediction of thrombosis in post-polycythemia vera and post-essential thrombocythemia myelofibrosis: a study on 1258 patients. Leukemia. Published online August 30, 2022. doi:10.1038/s41375-022-01673-3