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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%.
The baseline characteristics are shown in Table 1.
Table 1. Baseline patient characteristics*
Characteristics, % (unless otherwise specified) |
Patients |
Mean age, years |
66.3 |
Sex |
|
Male |
71.1 |
Female |
28.9 |
Disease subtype |
|
Essential thrombocythemia |
36.8 |
Primary myelofibrosis |
15.8 |
Post-essential thrombocythemia myelofibrosis |
5.3 |
Polycythemia vera |
28.9 |
Post-polycythemia vera myelofibrosis |
13.2 |
*Adapted from Fang, et al.1 |
The safety profile was manageable and four serious adverse events (SAE) were 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.
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