Ipsen agreed to acquire Kartos Therapeutics in a $450 million upfront deal, bringing navtemadlin—an MDM2-targeting, p53-restoring approach—into Ipsen’s pipeline. Kartos’ program has reached Phase 3 testing in myelofibrosis, targeting patients with suboptimal response to standard JAK therapy. Under the agreement, Ipsen will pay $450 million upfront and could make additional milestone payments that reach into the hundreds of millions, tied to development and regulatory progress. The deal is structured to support late-stage execution on navtemadlin while leveraging Ipsen’s commercial and clinical scale. The transaction matters because myelofibrosis remains a high-need oncology segment where second-line treatment options depend heavily on differentiation beyond existing JAK inhibition.