Of the roughly 600 patients now being recruited for a global Phase III trial called POIESIS, every single one has a form of myelofibrosis that has stopped responding to the only real option they had. That option is ruxolitinib. It works for many, at first.
But a significant proportion of patients get a suboptimal response. They stop treatment.
And after that, the numbers turn grim. Median overall survival for those patients hovers around one to two years. That is the hole Ipsen is trying to fill with a $900 million-plus acquisition of Kartos Therapeutics, a private biotech based in Redwood City, California.
The deal, announced June 29, hands Ipsen a late-stage drug called navtemadlin. It is an MDM2 inhibitor.
It works by restoring the tumor-suppressing function of p53, a protein that normally keeps cell growth in check but gets silenced in many cancers. Ipsen’s CEO David Loew said the move strengthens the company’s late-stage oncology pipeline and reflects a continued focus on bringing what he called transformational treatments to cancer patients. He expressed excitement about navtemadlin’s potential to define a new treatment paradigm, addressing what he described as a critical care gap.
Loew also said a new therapeutic option could arrive as early as 2028. The target population is specific: patients with intermediate and high-risk TP53 wild-type myelofibrosis who have a suboptimal response to ruxolitinib. That is a mouthful.
It means the patients still have their normal p53 gene — the drug needs that to work — and they have already tried and failed the standard treatment. The POIESIS trial is designed to enroll more than 600 patients across over 250 sites.
That is a big study for a niche blood cancer. It is testing navtemadlin as an add-on therapy to standard of care, not as a replacement. The idea is to layer the new drug on top of what patients are already taking, to see if it can push back against the disease where ruxolitinib alone falls short.
For the patients in that gap, the stakes are high. Ruxolitinib improves splenomegaly — that is an enlarged spleen, a hallmark of myelofibrosis — and it eases symptoms.
But it does not work for everyone, and when it stops working, the disease tends to move fast. The median survival numbers after discontinuation are stark: one to two years. Kartos has been working on navtemadlin for years.
The drug is still investigational. No regulatory approvals have been filed yet. Ipsen, headquartered in Paris and listed on Euronext with an ADR on the US market, is betting that the Phase III data will hold up and that the FDA will see a drug that fills a real need.
Oncologists who treat myelofibrosis have watched this space closely. The standard of care has not changed much in years.
Ruxolitinib was a breakthrough when it arrived, but the field has been waiting for something that can help the patients it leaves behind. Navtemadlin targets a different mechanism — not JAK inhibition, but MDM2 inhibition — which means it might work where JAK inhibitors stop working. The deal structure was not disclosed in full.
But the mechanics are straightforward: a private US biotech sells to a large French pharma. The asset is a single late-stage drug aimed at a defined patient population with a clear unmet need.
That is the kind of deal that analysts tend to call sensible, not splashy. Whether navtemadlin actually delivers is still an open question. The POIESIS trial is global, it is large, and it is running now.
If it works, Ipsen will have a new drug on the market by 2028. If it does not, the patients in that one-to-two-year survival window will still be waiting.
