PARIS, France & REDWOOD CITY, Calif., June 29, 2026
Ipsen has announced a definitive agreement to acquire Kartos Therapeutics, significantly strengthening its late-stage hemato-oncology pipeline with the addition of navtemadlin, an investigational oral MDM2 inhibitor currently being evaluated in a global Phase III clinical trial for myelofibrosis. Under the terms of the transaction, Ipsen will pay $450 million upfront, while Kartos shareholders may receive up to $1.3 billion in additional milestone payments tied to regulatory approvals and commercial performance. The acquisition reinforces Ipsen’s long-term oncology growth strategy by adding a promising late-stage therapy with the potential to address a major unmet medical need in patients who experience a suboptimal response to ruxolitinib, the current first-line standard of care for intermediate- and high-risk TP53 wild-type myelofibrosis. Expected to close by the end of the third quarter of 2026, subject to customary regulatory conditions, the transaction expands Ipsen’s portfolio of innovative cancer therapies while strengthening its leadership in hematologic malignancies.
Navtemadlin Targets Significant Unmet Need in Myelofibrosis
Navtemadlin is an investigational MDM2 inhibitor designed to restore the tumor-suppressing activity of the p53 pathway, offering a novel therapeutic mechanism for patients whose disease remains inadequately controlled with ruxolitinib. Although ruxolitinib effectively reduces spleen enlargement and symptom burden in many patients, a substantial proportion eventually develop inadequate responses or discontinue therapy, leaving limited treatment options and poor survival outcomes. Navtemadlin is being evaluated as an add-on therapy rather than a replacement, with the goal of converting suboptimal responders into clinically meaningful responders while potentially modifying the underlying disease biology.
Earlier Phase Ib/II clinical studies demonstrated encouraging results, including significant reductions in spleen volume, meaningful improvements in total symptom scores, decreased driver mutation burden, and improvements in bone marrow fibrosis. These findings support the scientific rationale for combining navtemadlin with standard JAK inhibition to achieve deeper and more durable therapeutic responses for patients living with this rare blood cancer.
Phase III Program Strengthens Ipsen’s Oncology Growth Strategy
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The ongoing global Phase III POIESIS trial represents the largest clinical study conducted in myelofibrosis, enrolling more than 600 patients across over 250 clinical sites worldwide. The study is evaluating whether adding navtemadlin to standard ruxolitinib therapy improves clinical outcomes compared with current treatment alone, with top-line results expected in 2027. If successful, Ipsen believes the therapy could establish a new treatment paradigm for patients experiencing inadequate responses to existing therapy and potentially become available as early as 2028, subject to regulatory approvals. Beyond the immediate addition of navtemadlin, the acquisition aligns with Ipsen’s strategy of expanding its oncology franchise through innovative external partnerships and acquisitions targeting therapies with significant clinical differentiation and commercial potential.
The transaction further strengthens Ipsen’s growing portfolio of transformational oncology medicines while expanding its presence in rare hematologic cancers, an area where substantial unmet medical need continues to exist. By combining Kartos Therapeutics’ innovative p53-targeting science with Ipsen’s global development and commercialization capabilities, the acquisition positions the company to accelerate the advancement of next-generation therapies for myelofibrosis and potentially improve long-term outcomes for patients facing limited treatment options. The agreement also highlights the continued momentum of strategic mergers and acquisitions within the biotechnology industry as companies invest in late-stage assets capable of delivering both scientific innovation and future commercial growth.
Source: Ipsen, Kartos Therapeutics press release
