Extreme thrombocytosis among young patients with myeloproliferative neoplasms (MPNs) was well controlled by interferon therapy. These findings, from a retrospective review of medical records, were published in Pediatric Blood and Cancer.

Records from 13 patients aged younger than 21 years with polycythemia vera (n=7) or essential thrombocythemia (ET; n=6) and treated with pegylated interferon (PEG) since 2005 at 6 institutions, were assessed for clinical outcomes.

Patients were aged median 11 years (interquartile range [IQR], 5.5-14.5) at diagnosis, began PEG therapy at age 14 years (IQR, 9.5-16), and 8 were girls. At baseline, 6 children had splenomegaly, 9 had extreme thrombocytosis, and 1 had splanchnic vein thrombosis. Most patients (n=6) had Janus kinase 2 (JAK2) V617F, 2 had JAK2-Exon-12, 1 had calreticulin (CALR) mutations, and 4 were triple-negative.

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PEG therapy lasted a median of 24 months (range, 10 to 168), at doses of 45-153 mg, administered every 1 to 4 weeks. A total of 5 children discontinued PEG due to thrombotic or bleeding events and 8 patients remained on PEG therapy at study conclusion.

Among the patients with extreme thrombocytosis, 8 had decreased platelet counts (<1000×109/L). The 2 patients with ET and a JAK2-Exon-12mutation did not show improved iron deficiency.

Some patients with JAK2V617F (n=3) showed improved allele burden (from 49% to 32.7% after 3 years, 53% to 25% after 2 years, and 26% to 21% after 1 year).

This study was limited by the low sample size and the variable and gender-specific symptom variation among younger patients, making it unclear whether these results may be generalizable.

These data indicated 89% of pediatric patients with extreme thrombocytosis had resolution following PEG therapy and 62% were able to remain on PEG despite adverse events.

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.


Kucine N, Bergmann S, Krichevsky S, et al. Use of pegylated interferon in young patients with polycythemia vera and essential thrombocythemia. Pediatr Blood Cancer. Published online December 31, 2020. doi:10.1002/pbc.28888