Paris, France | August 21, 2026
Ipsen announced the completion of its acquisition of Kartos Therapeutics, strengthening its late-stage oncology portfolio with navtemadlin, an investigational oral MDM2 inhibitor currently being evaluated in a Phase III clinical program for myelofibrosis. The transaction adds a late-stage targeted therapy to Ipsen’s oncology pipeline and expands the company’s focus on developing treatment strategies for patients whose disease remains inadequately controlled with existing standard-of-care therapy.
Navtemadlin Advances in Phase III Myelofibrosis Program
Navtemadlin is being developed as an add-on therapy to ruxolitinib for patients with myelofibrosis who have a suboptimal response to ruxolitinib. The investigational therapy is being evaluated in the Phase III POIESIS study, which is designed to assess whether adding navtemadlin to ruxolitinib can improve clinical outcomes compared with ruxolitinib alone. Navtemadlin is an oral MDM2 inhibitor, representing a targeted approach intended to address disease biology beyond JAK pathway inhibition. Early clinical findings cited by Ipsen suggest the combination may improve responses in patients with intermediate- and high-risk TP53 wild-type myelofibrosis, while potentially providing a disease-modifying benefit. The Phase III program will be important in determining whether these earlier observations translate into clinically meaningful benefits in a larger patient population.
Myelofibrosis Creates Significant Treatment Need
Myelofibrosis is a serious myeloproliferative neoplasm associated with bone marrow fibrosis, abnormal blood-cell production and splenomegaly. The disease can produce substantial symptoms, including fatigue and night sweats, while progressive impairment of bone marrow function can contribute to bone marrow failure. Patients may also face a risk of transformation to acute myeloid leukemia. Ruxolitinib, a JAK inhibitor, remains a first-line standard treatment, but a significant proportion of patients have an inadequate initial response or eventually discontinue therapy. Ipsen estimates that approximately 50% to 75% of patients discontinue ruxolitinib within three years, highlighting the need for additional treatment approaches capable of improving and sustaining clinical responses. The majority of patients are classified as intermediate- or high-risk at diagnosis, while more than 95% are reported to have TP53 wild-type disease, supporting the potential relevance of an MDM2-targeted strategy in this population.
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Acquisition Adds Late-Stage Oncology Opportunity
The completion of the Kartos acquisition gives Ipsen direct ownership of navtemadlin and its ongoing Phase III development program, providing the company with a potentially important late-stage asset in hematologic oncology. The transaction also strengthens Ipsen’s strategy of combining internal research with external innovation to expand its portfolio across Oncology, Rare Disease and Neuroscience. For cGxP.wire, the key development is the transition of navtemadlin into Ipsen’s late-stage pipeline at a point when the POIESIS Phase III trial is positioned to determine whether the investigational MDM2 inhibitor can improve outcomes for patients inadequately responding to ruxolitinib. While early data provide a rationale for the approach, the therapy remains investigational, and the Phase III results will ultimately determine its clinical and regulatory potential. The acquisition therefore represents a significant pipeline expansion in oncology, with navtemadlin becoming a central late-stage development opportunity for Ipsen in myelofibrosis.
Source:Ipsen press relese
