Seagen

Seagen

Seagen was founded in 1997 by Clay Siegall, a scientist who pioneered the antibody-drug conjugate (ADC) platform. Siegall led the company through its IPO in 2001 and the approval of its first drug, Adcetris, in 2011. The company's wealth was built on the commercial success of Adcetris and subsequent ADC candidates (per the company's SEC filings). Seagen's strategy centered on developing ADCs — cancer therapies that deliver a toxic payload directly to tumor cells. Its approved products include Adcetris (brentuximab vedotin, for lymphoma) and Padcev (enfortumab vedotin, for bladder cancer, co-developed with Astellas). Beyond those, Seagen had a pipeline of early-stage candidates targeting solid tumors and hematologic malignancies. The company operated across phase 1 through registration-stage trials and relied on internal discovery, not external deal flow, for its pipeline. The firm's scale peaked with its $43B acquisition by Pfizer, announced in March 2023 and completed in December 2023 (per Pfizer, December 2023). At the time, Seagen employed over 3,000 people across its Bothell headquarters and offices in New York, Rockville, Cambridge (MA), Hoboken, Montreal, and Hellerup, Denmark. The company also maintained a philanthropic arm, Seagen Foundation, which focused on cancer-related giving. Seagen's structural differentiator was its proprietary ADC platform, which gave it a rare position as both a drug developer and a technology licensor. The platform generated royalties from partnerships with Takeda, Astellas, and others — a dual revenue stream uncommon among mid-cap biotechs. Post-acquisition, Seagen no longer exists as an independent entity, but its ADC platform now operates within Pfizer's Oncology unit.