Ipsen has agreed to buy Kartos Therapeutics, a US biotech, in a deal worth up to $1.75 billion. The French drugmaker pays $450 million upfront. Another $1.3 billion depends on development and commercial milestones.
What it gets is navtemadlin, also known as KRT-232, an investigational pill for myelofibrosis. The disease is a rare blood cancer in which scarring of the bone marrow disrupts blood cell production, enlarges the spleen and brings on debilitating symptoms.
Most treatment today centres on Jakafi (ruxolitinib), a JAK inhibitor developed by Incyte. It has changed care for many patients by shrinking the spleen and easing symptoms. But a significant share eventually respond poorly or stop taking it altogether. Navtemadlin is aimed at them.
A different target
The drug does not work like a JAK inhibitor. It blocks a protein called MDM2, which restores the activity of the tumour suppressor p53 in patients whose cancers carry the wild-type version of the TP53 gene. And it is not meant to replace Jakafi. It is being developed as an add-on for patients whose disease is no longer under adequate control.
The lead programme is the Phase III POIESIS trial. It enrols patients with intermediate- and high-risk TP53 wild-type myelofibrosis who have had a suboptimal response to Jakafi.
Earlier Phase Ib/II results looked encouraging, though the group was small. Among 19 patients who took navtemadlin alongside Jakafi, 42% saw spleen volume fall by at least 25% after 24 weeks. For 32%, the reduction reached 35%, the stricter measure. Another 32% reported at least a 50% improvement in total symptom score.
Ipsen chief executive David Loew said navtemadlin could set “a new treatment paradigm” for patients who respond inadequately to the current standard of care. A commercial launch could come as early as 2028, he said, if development goes well.
The Kartos purchase follows another oncology deal. In October 2025 Ipsen agreed to buy ImCheck Therapeutics for up to €1 billion, gaining an experimental immuno-oncology antibody called ICT01. If POIESIS confirms the earlier findings, navtemadlin would give Ipsen a product in haematological oncology and doctors a new option for patients who run out of choices on JAK inhibitors alone.
