Ipsen agrees to buy Kartos Therapeutics for up to $1.75 billion

Ipsen said on June 29, 2026 that it has agreed to acquire Kartos Therapeutics for up to $1.75 billion, a deal that would add a late-stage myelofibrosis drug to the French company’s oncology pipeline.

The transaction calls for Ipsen to pay $450 million upfront and as much as $1.3 billion more in milestone payments tied to regulatory and sales outcomes. The companies said the deal is expected to close by the end of the third quarter of 2026, subject to customary closing conditions.

Why Kartos matters

Kartos’ lead asset is navtemadlin, an experimental treatment for myelofibrosis, a rare blood cancer with limited treatment options. Ipsen said the drug could become a new therapeutic option as early as 2028 if development goes as planned.

The deal gives Ipsen a potential growth driver at a time when large drugmakers are using acquisitions to deepen their pipelines and offset pressure from older products.

Ipsen’s oncology push

Ipsen has been building out its oncology business through dealmaking, including its recent acquisition of ImCheck Therapeutics. The Kartos purchase extends that strategy by bringing in a late-stage asset with a clearer path toward a potential launch than an early research program.

Ipsen said the acquisition should begin contributing to core operating profit from 2029 and have limited dilution to its 2026 guidance.

What to watch

Investors will be looking for the final transaction documents, any regulatory or shareholder approvals that may be required, and further detail on the milestone structure.

Another key question is whether navtemadlin can advance through the remaining clinical and regulatory steps on the timeline Ipsen described.