Pfizer has signed a co-development and licence agreement with Medicus Pharma granting global development, manufacturing and commercialisation rights to PF-08046031, a CD228-targeted antibody-drug conjugate (ADC) with an MMAE payload at a drug-to-antibody ratio (DAR) of 4, originally derived from Seagen's SGN-CD228A and inherited through Pfizer's USD 43 billion acquisition of Seagen in 2023.

Medicus pays USD 12 million upfront and USD 15 million at the one-year anniversary, with Pfizer returning USD 2 million as development funding, while Pfizer remains eligible for more than USD 1 billion in development, regulatory and commercial milestones plus low double-digit tiered royalties on net sales, while retaining the right to re-engage financially at the pivotal trial stage.

Preclinical data showed tumour regression of 87% to 90% at 6 mg/kg in melanoma models, but Pfizer's Phase I study in advanced melanoma and other solid tumours, opened in January 2025, was terminated in March 2026 for strategic reprioritisation rather than safety failure, leaving human efficacy effectively unproven. The structure is a risk-transfer option: Medicus absorbs near-term clinical burn and financing risk on a Seagen-grade asset package, while Pfizer sheds early-stage cost, keeps the patent estate, and preserves upside through milestones, royalties, and a re-entry clause.