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TAMARIN trial: Tamoxifen for the treatment of MPN

Jan 31, 2024
Learning objective: After reading this article, learners will be able to recall key findings from the TAMARIN trial.

Test your knowledge! Take our quick quiz before and after you read this article to find out if you improved your knowledge. Results help us to improve content and continually provide open-access education.

Many therapies for myeloproliferative neoplasms (MPN) address symptom improvement without a focus on reduction in tumor size.1 Tamoxifen, a selective estrogen receptor modulator, has been shown to induce apoptosis in multipotent hematopoietic progenitors whilst sparing normal hematopoietic stem cells; therefore, it is under investigation to target tumor size in patients with stable MPN and without previous thrombotic events.1

Below, we summarize the phase II TAMARIN study (EudraCT 2015-005497-38) investigating tamoxifen in patients with stable MPN; no prior thrombotic events; and mutated JAK2V617F, CALRins5, or CALRdel52 peripheral blood allele burden ≥20%.

TAMARIN study design1

  • In total, 38 patients were enrolled
  • The primary outcome was a ≥50% decrease in mutant allele burden in peripheral blood at 24 weeks
  • Secondary outcomes included a ≥25% decrease in mutant allele burden at 24 weeks and toxicities


The baseline characteristics are shown in Table 1.

Table 1. Baseline patient characteristics*

Characteristics, % (unless otherwise specified)

(N = 38)

Mean age, years







Disease subtype

              Essential thrombocythemia


              Primary myelofibrosis


              Post-essential thrombocythemia           myelofibrosis


              Polycythemia vera


              Post-polycythemia vera myelofibrosis


*Adapted from Fang, et al.1


  • Most patients (84%) completed the 24-week treatment plan
  • Overall, three patients met the primary outcome
    • Three patients achieved ≥50% reduction in mutant allele burden
  • Five patients showed a 25% decrease in mutant allele burden at 24 weeks
    • Three of these patients carried the JAK2V617F mutation
    • The two remaining patients carried CALRdel52 and CALRins5 mutations, but these mutations also require increased MPL-JAK-STAT activation to be pathogenic.
  • Six patients remained on treatment beyond 48 weeks


The safety profile was manageable and four serious adverse events (SAE) were reported:

  • urinary infection (n = 2) and intracranial hemorrhage (n = 1) not considered related to treatment;
  • vascular disorders (n = 1) considered possibly related to treatment; and
  • no deaths reported.


Tamoxifen was shown to reduce mutant allele burden in a subset of MPN patients who could be identified by hematopoietic stem cell transcriptomic signature before treatment. The primary endpoint (≥50% decrease in mutant allele burden in peripheral blood at 24 weeks) of this phase II study was met and observed in 3 patients. These findings advocate for future clinical studies to test the effectiveness of other selective estrogen receptor modulators in MPN, specifically the Janus kinase 2-signaling pathway.

  1. Fang Z, Fattori GC, McKerrell T, et al. Tamoxifen for the treatment of myeloproliferative neoplasms: A phase II clinical trial and exploratory analysis. Nat Commun. 2023;14(1):7725. DOI: 1038/s41467-023-43175-5


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