FDA approves Mimrylo for polycythaemia vera, a new class of treatment for the rare blood cancer

The US Food and Drug Administration has granted approval to Mimrylo (rusfertide), a hepcidin mimetic co-developed by Protagonist Therapeutics and Takeda, for the treatment of polycythaemia vera (PV) — a rare myeloproliferative neoplasm characterised in the large majority of cases by an acquired gain-of-function mutation in the JAK2 gene (most commonly JAK2 V617F).

PV causes the bone marrow to overproduce red blood cells, raising the risk of thrombotic events. Existing management has relied on phlebotomy, hydroxyurea, and JAK inhibitors such as ruxolitinib. Rusfertide takes a different mechanistic approach: by mimicking hepcidin, the peptide hormone that regulates iron availability, it restricts the iron supply required for erythropoiesis, thereby controlling haematocrit without directly targeting the JAK–STAT signalling axis.

The approval represents the first regulatory clearance for a hepcidin mimetic in a haematological malignancy and may be of interest to oncologists and haematologists managing patients with PV, particularly those with inadequate haematocrit control on current agents. The genetic basis of PV — somatic JAK2 mutations detectable by molecular testing — means that genetic counsellors involved in the diagnostic workup of myeloproliferative neoplasms may also note this addition to the therapeutic landscape. Researchers working on iron regulation, erythropoiesis, or myeloid disease genetics will find the mechanistic rationale of independent interest.