Ipsen completes acquisition of Kartos Therapeutics, strengthening late-stage Oncology pipeline

PARIS, FRANCE, 21 AUGUST 2026 – Ipsen (Euronext: IPN; ADR: IPSEY) announced today it has completed the acquisition of Kartos Therapeutics, a clinical-stage biopharmaceutical company adding late-stage MDM2 inhibitor navtemadlin in Phase III clinical development in myelofibrosis.

About navtemadlin Navtemadlin is an investigational oral MDM2 inhibitor being developed as an add-on therapy to ruxolitinib for patients with myelofibrosis who have a suboptimal response to ruxolitinib. The Phase III POIESIS study is evaluating whether the addition of navtemadlin could improve clinical outcomes compared with ruxolitinib alone in this patient population. Early clinical data demonstrate navtemadlin has the potential to transform suboptimal responses to standard of care ruxolitinib into clinically meaningful responses in patients with intermediate and high risk TP53wt myelofibrosis, to provide both enhanced clinical outcomes and potential disease-modifying benefit.

About myelofibrosis Myelofibrosis is a myeloproliferative neoplasm, frequently linked to alterations in the JAK/STAT pathway, in which patients develop bone marrow fibrosis due to the abnormal proliferation of hematopoietic stem cells and secretion of fibrogenic cytokines. As marrow function declines, blood production shifts to other organs, most often the spleen, leading to splenomegaly. Myelofibrosis is characterized by bone marrow failure, fibrosis, splenomegaly and a high symptom burden that can significantly affect quality of life, including fatigue, night sweats and other progressive symptoms. It also carries a risk of transformation to acute myeloid leukemia. The median age at diagnosis is approximately 67–69 years and the condition affects around 1.5 per 100,000 people in the U.S. and Europe. Approximately 75–89% of patients are intermediate- or high-risk at diagnosis and more than 95% are TP53wt. Ruxolitinib, a JAK inhibitor, is the first-line standard of care; however, it is estimated that a significant proportion of patients have an initial suboptimal response and approximately 50%-75% discontinue treatment after three years. Median overall survival is typically one to two years after treatment discontinuation, underscoring the need for new strategies that can increase the number of patients that can achieve optimal clinical outcomes.

About Ipsen We are a global biopharmaceutical company with a focus on bringing transformative medicines to patients in three therapeutic areas: Oncology, Rare Disease and Neuroscience. Our pipeline is fueled by internal and external innovation and supported by nearly 100 years of development experience and global hubs in the U.S., France and the U.K. Our teams in more than 40 countries and our partnerships around the world enable us to bring medicines to patients in more than 100 countries.

Ipsen is listed in Paris (Euronext: IPN) and in the U.S. through a Sponsored Level I American Depositary Receipt program (ADR: IPSEY).