Ipsen acquires Kartos for $1.75B to add Jakafi combo therapy navtemadlin in myelofibrosis

Ipsen is acquiring privately held U.S. biotech Kartos Therapeutics in a deal valued at up to $1.75 billion, with an upfront payment of $450 million and potential milestone payments of up to $1.3 billion tied to regulatory approvals and sales performance.

The transaction, announced on June 29, 2026, is expected to close by the end of the third quarter of 2026, subject to customary conditions including U.S. antitrust review (Hart-Scott-Rodino).

The centerpiece of the acquisition is navtemadlin, an oral MDM2 inhibitor being developed as an add-on therapy to Incyte's Jakafi (ruxolitinib) in patients with intermediate- and high-risk TP53 wild-type myelofibrosis who have a suboptimal response to ruxolitinib.

Earlier phase 1b/2 trial data showed that navtemadlin added to Jakafi in patients who responded poorly to Jakafi led to spleen volume reductions of at least 25% in 42% of patients and at least 50% symptom score improvement in 32% of patients at week 24.

Navtemadlin is now being evaluated in the ongoing phase 3 POIESIS trial, which aims to enroll over 600 patients across more than 250 sites; top-line data are expected in 2027, and Ipsen projects the drug could become a new therapeutic option as early as 2028.

Ipsen expects the acquisition to be accretive to core operating income starting in 2029, with only limited dilution to its 2026 earnings guidance.