Ipsen agreed to buy Kartos Therapeutics for $450 million upfront as it builds out late-stage blood cancer exposure through navtemadlin, an investigational oral MDM2 inhibitor. The acquisition is structured with additional milestone payments up to $1.3 billion, with Ipsen positioning navtemadlin as an add-on approach in intermediate- and high-risk TP53 wild-type myelofibrosis where patients have suboptimal response to ruxolitinib. Ipsen described navtemadlin’s Phase 3 POIESIS program as open and recruiting, targeting more than 600 patients across more than 250 sites. Kartos highlighted the unmet need in symptomatic or persistently splenomegaly patients despite JAK inhibition. The deal is the latest step in Ipsen’s late-stage oncology pipeline strategy and adds a near-term regulatory pathway as POIESIS approaches topline timing.