Ipsen Acquiring Kartos Therapeutics, Bolstering Late-Stage Cancer Pipeline

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Ipsen is acquiring Kartos Therapeutics, and with it navtemadlin, an investigational add-on treatment for myelofibrosis, a rare, serious blood cancer.

Navtemadlin is an investigational MDM2 inhibitor that restores natural tumor-suppressing function in p53. In myelofibrosis, p53 is a critical tumor suppressor. Existing data on navtemadlin show strong therapeutic potential for intermediate and high-risk TP53 wild-type myelofibrosis, added to standard-of-care ruxolitinib.

Currently, ruxolitinib improves splenomegaly and myelofibrosis-related symptoms. However, many patients experience suboptimal response, leading to discontinuation of treatment. When that happens, patient outcomes are dire: Median overall survival after that point is approximately 1–2 years.

Myelofibrosis Symptoms, Further Cancer Risk

Even disregarding the survival rate, myelofibrosis leads patients to develop bone marrow fibrosis, shifting blood production to other organs. Most common among these is the spleen, often resulting in splenomegaly. Additional symptoms—other than bone marrow failure and fibrosis, include progressive quality-of-life issues such as fatigue and night sweats.

Also, myelofibrosis carries with it the risk of transforming into acute myeloid leukemia.

Navtemadlin is now being evaluated as an add-on to ruxolitinib in a Phase III trial (POIESIS) enrolling over 600 patients.

Ipsen Looking Forward to Kartos Merger

“We are excited by the potential of navtemadlin to define a new treatment paradigm,” Ipsen CEO David Loew said. “[This addresses] a critical care gap, offering the potential for a new therapeutic option as early as 2028. This further strengthens our late-stage oncology pipeline, reflecting our continued focus on bringing transformational treatments to people living with cancer.”

The Kartos acquisition is actually a merger for which Ipsen—through a subsidiary—will pay $450 million upfront at closing. Shareholders of Kartos Therapeutics are eligible to receive additional milestone payments totaling up to $1.3 billion.