Ipsen and Kartos Therapeutics announced that they have entered into a definitive merger agreement under which Ipsen will acquire Kartos Therapeutics. The deal adds navtemadlin, a late-stage rare blood cancer asset in Phase III development, to Ipsen’s hemato-oncology pipeline.
Under the terms of the agreement, Ipsen will pay $450 million upfront at closing through a wholly owned subsidiary.
Kartos Therapeutics shareholders are also eligible to receive additional milestone payments of up to $1.3 billion, including a significant regulatory approval milestone and sales-based milestones.
The transaction is expected to close by the end of the third quarter of 2026, subject to customary closing conditions, including expiration of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act.
The acquisition is expected to be accretive to Ipsen’s core operating income from 2029, with limited dilution to 2026 full-year guidance.
Navtemadlin is an investigational oral MDM2 inhibitor designed to restore the natural tumor-suppressing function of p53, which is considered a critical tumor suppressor in myelofibrosis.
Ipsen said navtemadlin has shown strong therapeutic potential for intermediate- and high-risk TP53 wild-type myelofibrosis as an add-on treatment for patients with a suboptimal response to standard-of-care ruxolitinib.
Ruxolitinib is the current standard of care and improves splenomegaly and myelofibrosis-related symptoms. However, Ipsen noted that a significant proportion of patients have a suboptimal response, leading to treatment discontinuation.
Patient outcomes after ruxolitinib discontinuation remain poor, with median overall survival of approximately one to two years.
Navtemadlin is being evaluated in the global Phase III POIESIS trial as an add-on therapy to ruxolitinib in patients with intermediate- and high-risk TP53 wild-type myelofibrosis who have a suboptimal response to ruxolitinib.
The POIESIS trial is designed to enroll more than 600 patients across more than 250 sites, and top-line data are expected in 2027.
The trial builds on earlier clinical evidence, including a Phase Ib/II trial in which add-on navtemadlin demonstrated clinically meaningful and potentially disease-modifying activity in myelofibrosis patients with a suboptimal response to ruxolitinib.
Data presented at the European Hematology Association Congress in 2023 showed that at Week 24, 42% of patients with a suboptimal response to ruxolitinib achieved at least a 25% reduction in spleen volume, while 32% achieved at least a 35% reduction in spleen volume.
The data also showed that 32% achieved a total symptom score improvement of at least 50%.
Ipsen said the data showed potential disease-modifying activity, with 71% of evaluable patients achieving at least a 20% reduction of driver variant allele frequency and 57% showing an improvement in bone marrow fibrosis by central review of at least one grade by Week 24.
Myelofibrosis is a rare blood cancer and myeloproliferative neoplasm frequently linked to alterations in the JAK/STAT pathway.
The disease is characterized by bone marrow failure, fibrosis, splenomegaly, and a high symptom burden that can significantly affect quality of life. It also carries a risk of transformation to acute myeloid leukemia.
Ipsen said the median age at diagnosis is approximately 67 to 69 years, and the condition affects around 1.5 per 100,000 people in the U.S. and Europe.
Orrick Herrington & Sutcliffe is acting as legal counsel to Ipsen. Goldman Sachs and PJT Partners are serving as financial advisors to Kartos Therapeutics, and DLA Piper is serving as Kartos Therapeutics’ legal counsel.
Ipsen is a global biopharmaceutical company focused on oncology, rare disease, and neuroscience. Kartos Therapeutics is a clinical-stage biopharmaceutical company developing navtemadlin as a potential best-in-class MDM2 inhibitor.
KEY QUOTES:
“This acquisition further strengthens our late-stage oncology pipeline and reflects our continued focus on bringing transformational treatments to people living with cancer. We are excited by the potential of navtemadlin to define a new treatment paradigm for patients with myelofibrosis who have a suboptimal response to current standard of care, addressing a critical care gap and offering the potential for a new therapeutic option as early as 2028.”
David Loew, CEO of Ipsen
“As a treating clinician who cared for more than a thousand patients with myelofibrosis, I have seen first-hand the significant care gap for patients with myelofibrosis who remain symptomatic or have persistent splenomegaly despite ruxolitinib treatment. Navtemadlin has the potential to enhance the existing standard of care through an add-on approach designed to move patients with a suboptimal response into a clinical responder group by optimizing their care. We believe this innovative treatment paradigm could meaningfully improve outcomes for patients while avoiding unnecessary over-treatment of those already responding well.”
Srdan Verstovsek, MD, PhD, Chief Medical Officer of Kartos Therapeutics
“Myelofibrosis remains a serious and rare blood cancer associated with a substantial symptom burden and progressive splenomegaly that significantly impact quality of life. The clinical rationale for combining navtemadlin with ruxolitinib is very compelling, and the emerging data suggest the synergistic potential to deepen responses and address the underlying biology of the disease.”
John Mascarenhas, Professor of Medicine at the Icahn School of Medicine at Mount Sinai and Director of the Center of Excellence for Blood Cancers and Myeloid Disorders
“The Phase III POIESIS trial has the potential to redefine how we treat patients with myelofibrosis. It is the largest trial conducted in this disease and uniquely designed to reflect real-world clinical practice. The trial evaluates how adding navtemadlin can deliver more clinically meaningful and durable responses, thereby addressing a critical unmet need. I am excited by the prospect of navtemadlin delivering disease modifying benefits, ushering an era of rational combination therapies for those with suboptimal response to standard therapy, and targeting complementary disease pathways beyond JAK inhibition alone in myelofibrosis.”
Dr. Pankit Vachhani, Associate Professor of Medicine and Director of Clinical Research Unit at the University of Alabama at Birmingham and Global Principal Investigator of POIESIS
