Pfizer will pay $229 in cash per Seagen share, a 32.7% premium to Friday's closing price. The offer is also a nearly 42% premium to the stock's close on Feb. 24, a day before the Wall Street Journal first reported on a possible deal.
Pfizer has hit the deals route in its quest to mitigate the impact from an anticipated $17 billion drop in revenue by 2030 due to patent expirations for top drugs and decline in demand for its COVID products.
"While Pfizer still has more firepower to do deals, we think integrating such a large company could make (Pfizer) take a pause on M&A front," Wells Fargo analyst Mohit Bansal said in a research note.
Washington-based Seagen is a pioneer of antibody-drug conjugates (ADCs), which work like "chemo guided missiles" designed for a targeted destructive effect and spare healthy cells.
Pfizer's portfolio of oncology therapies includes 24 approved drugs, including breast cancer treatment Ibrance.
The companies expect to complete the deal in late 2023 or early 2024.
The deal is unlikely to face major antitrust challenges as the companies do not have major overlapping products, Bansal said, but could still face some scrutiny due to its size.
Pfizer rival Merck & Co Inc (MRK.N) and Seagen were in advanced deal talks last year but that reportedly collapsed over fears of tough antitrust scrutiny.