In a March 2023 interview, Seagen co-founder Clay Siegall welcomed Pfizer’s planned acquisition of the cancer-drug company and described his new role leading Morphimmune. The deal was announced at $229 per share in cash, but Siegall was no longer Seagen’s CEO or chair when it was announced: he had left those roles in May 2022. Pfizer completed the acquisition in December 2023, and Siegall later moved from Morphimmune to lead Immunome.
What Siegall said about Pfizer’s proposed Seagen deal
GeekWire interviewed Siegall on March 23, 2023, ten days after Pfizer announced its agreement to acquire Seagen. The Q&A was edited for brevity and clarity, and it presents Siegall’s own perspective—not an independent assessment of the transaction.
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“That one of the biggest pharmaceutical companies in the world, Pfizer, is buying into this is fantastic,” Siegall told GeekWire. “It shows that ADCs have come of age.” He also said he was “totally delighted” with his new enterprise and intended to build another company. Those comments reflected his view at the time, not a measure of the deal’s later financial or clinical results.
What Pfizer agreed to pay—and what happened next
Pfizer and Seagen announced the definitive agreement on March 13, 2023. Pfizer said it would pay $229 in cash for each Seagen share, at an approximately $43 billion total enterprise value. Its announcement presented Seagen’s oncology portfolio and antibody-drug-conjugate expertise as complementary to Pfizer’s capabilities. These were the announced terms and Pfizer’s stated rationale; they should not be confused with forecasts of future performance.
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Pfizer completed the acquisition on December 14, 2023, on the announced $229-per-share cash terms and approximately $43 billion enterprise value, according to Pfizer’s completion announcement.
At announcement, Pfizer said Seagen expected approximately $2.2 billion in revenue for 2023 and Pfizer forecast that Seagen could contribute more than $10 billion in risk-adjusted revenue in 2030. Those were estimates and a forward-looking forecast published in 2023, not confirmed results.
Why Seagen mattered to the deal
Siegall co-founded Seattle Genetics in 1997; the company later became Seagen. GeekWire reported that he helped take it public in 2001 and oversaw the approval of four oncology medicines. Pfizer’s 2023 announcement named those medicines as ADCETRIS (brentuximab vedotin), PADCEV (enfortumab vedotin), TIVDAK (tisotumab vedotin), and TUKYSA (tucatinib).
Three of the four—ADCETRIS, PADCEV, and TIVDAK—are antibody-drug conjugates, or ADCs. An ADC uses an antibody to recognize a target on cells and deliver an active payload, such as a cancer-killing drug. Pfizer described the approach as designed to preferentially kill cancer cells while limiting off-target toxicity; that design goal does not mean a treatment eliminates toxicity or works for every patient.
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Siegall was no longer running Seagen when Pfizer announced the deal
The timing matters: although he was Seagen’s founder and former leader, Siegall was not in charge of the company as the Pfizer transaction came together. GeekWire reported that he resigned as CEO and chair in May 2022. An SEC-filed Immunome proxy later records his Seagen CEO service through May 2022.
In the interview, Siegall acknowledged the change after 25 years at the company: “There is a little strangeness to it. But you know what, it’s OK.” He also said, “It’s not the money that’s most important, it’s the lives that are saved.” These are his stated reflections, not claims about the deal’s eventual impact.
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At the time of the GeekWire interview, Siegall was president and CEO of Morphimmune, which the publication described as a Purdue University spinout with plans to expand in Seattle. He characterized the challenge of building companies as a matter of time rather than access to capital: “You can get money to build companies.”
A later SEC-filed Immunome proxy, published in 2025, provides the subsequent chronology: it records Siegall as Morphimmune’s CEO from January 2023 until October 2023, before Morphimmune merged with Immunome. The filing says he became Immunome’s president, CEO, and board chair in October 2023. The interview’s description of Morphimmune therefore captures his role in March 2023, not his current position.
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The Q&A is useful for understanding how Seagen’s founder viewed Pfizer’s announcement and what he was doing in biotech in March 2023. It is not an independent evaluation of Pfizer’s acquisition rationale, a report on the subsequent financial performance of Seagen’s medicines, or an assessment of Morphimmune’s scientific pipeline. Pfizer’s deal forecasts should be read as forecasts, while Siegall’s comments should be read as his perspective.
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