Swedish Orphan Biovitrum (Sobi) has said it will acquire CTI BioPharma for approximately $1.7bn, marking a notable expansion to the Swedish drugmaker's rare haematology pipeline.

The deal will grant Sobi access to the US biopharma’s recently-approved Vonjo (pacritinib), a novel oral kinase inhibitor for patients with myelofibrosis and severe thrombocytopenia.

The drug was granted accelerated approval by the US Food and Drug Administration (FDA) in February last year to treat adults with intermediate or high-risk primary or secondary myelofibrosis with low platelet counts.

This was based on positive results from a phase 3 trial of Vonjo in patients with myelofibrosis. Results showed that 29% of patients receiving Vonjo had a reduction in spleen volume of at least 35% compared to 3% of patients receiving best available therapy.

Sobi said Vonjo will be ‘highly complementary’ to Doptelet (avatrombopag), its oral thrombopoietin receptor agonist which also addresses rare haematological platelet disorders.

Guido Oelkers, Sobi’s president and chief executive officer, said: “CTI represents a perfect fit for Sobi’s haematology franchise today, adding a powerful and highly differentiated new product that will make a significant difference for patients.”

“The combination of the talented team at CTI, together with Sobi’s broad US and global haematology capabilities, will help get this much needed new therapy to patients faster and more effectively,” Oelkers added.

Under the terms of the agreement, Sobi will make a tender offer for $9.10 per CTI share, a premium of 89% the company's closing price of $4.82 earlier this week. The transaction is expected to close in the third quarter of this year.

Adam Craig, president, chief executive officer and interim chief medical officer of CTI BioPharma, said: "We are delighted to announce this transaction, which delivers a compelling all-cash premium to our shareholders, while positioning CTI to unlock the full potential of Vonjo in treating myeloproliferative disease."

The deal comes a few months after Sobi and partner Sanofi’s once-weekly haemophilia A treatment, Altuviiio, was approved by the FDA for the prevention and on-demand treatment to control bleeding episodes, as well as for surgery management for adults and children with the disease.