Under the terms of a merger agreement, Pfizer will pay $229 per Seagen share, for a total of $43 billion. The transaction was unanimously approved by the boards of directors of both firms.

Pfizer expects to finance the transaction substantially through $31 billion of new, long-term debt, and the balance from a combination of short-term financing and existing cash. The companies expect to complete the transaction in late 2023 or early 2024.

The proposed combination will double Pfizer's early-stage oncology clinical pipeline, contributing Seagen's specialization in antibody-drug conjugate (ADC) technology to Pfizer's extensive cancer portfolio.

ADCs work across a broad range of cancers to preferentially kill cancer cells, thereby limiting off-target toxicity. Seagen's portfolio includes three ADCs -- Adcetris (brentuximab vedotin), Padcev (enfortumab vedotin), and Tivdak (tisotumab vedotin) -- as well as the drug Tukysa (tucatinib).

Seagen anticipates $2.2 billion of revenue in 2023, a year-over-year increase of approximately 12%. Taking into consideration the expected growth trajectories for these medicines along with drug candidates that could emerge from Seagen's pipeline, Pfizer believes that Seagen could contribute more than $10 billion in risk-adjusted revenues in 2030, with the potential for significant growth beyond 2030.