Arvinas, Inc. and Pfizer Inc. announced a global collaboration to develop and commercialize ARV-471, an investigational oral PROTAC® (PROteolysis TArgeting Chimera) estrogen receptor protein degrader. The estrogen receptor is a well-known disease driver in most breast cancers. ARV-471 is currently in a Phase 2 dose expansion clinical trial for the treatment of patients with estrogen receptor (ER) positive /human epidermal growth factor receptor 2 (HER2) negative (ER+/HER2-) locally advanced or metastatic breast cancer. Under the terms of the agreement, Pfizer will pay Arvinas $650 million upfront. Separately, Pfizer will make a $350 million equity investment in Arvinas. The companies will equally share worldwide development costs, commercialization expenses, and profits. ER is the primary driver of hormone receptor (HR) positive breast cancer, which is the most common breast cancer subtype. Endocrine therapy is a backbone of ER+ breast cancer treatment and is used as monotherapy or as combination therapy as a standard of care across treatment settings. Arvinas and Pfizer are seeking to develop ARV-471 as the potential endocrine therapy of choice for patients and their physicians. Interim data presented in December 2020 from the ongoing Phase 1 dose escalation clinical trial of ARV-471 in patients with locally advanced or metastatic ER+/HER2- breast cancer indicated its potential as a novel oral ER targeted therapy. This study has enrolled heavily pretreated patients, with all patients having received prior treatment with cyclin-dependent kinase (CDK) 4/6 inhibitors. Despite the advanced stage of disease and heavy pretreatment, these interim data, as of December 2020, demonstrated that ARV-471 can promote substantial ER degradation and exhibits an encouraging clinical efficacy and tolerability profile. ARV-471 currently is being evaluated as a treatment for metastatic breast cancer in a Phase 1 dose escalation study, a Phase 1b combination study with Pfizers IBRANCE® (palbociclib), and a Phase 2 monotherapy dose expansion study (VERITAC). Arvinas and Pfizer expect to initiate two additional trials of ARV-471 in 2021, including a second Phase 1b combination trial with everolimus and a trial in the neoadjuvant setting. In 2022, Arvinas and Pfizer expect to initiate Phase 3 studies across lines of therapy in metastatic breast cancer, including combinations with IBRANCE, followed by pivotal studies in the early breast cancer setting. The two companies had previously announced in 2018 a separate research collaboration and license agreement for the discovery and development of drug candidates using Arvinas PROTAC technology. The agreement is a worldwide co-development and co-commercialization collaboration. ARV-471 is wholly owned by Arvinas and under the financial terms of the agreement, Pfizer will pay Arvinas$650 million upfront. Separately, Pfizer will invest $350 million in Arvinas, receiving approximately 3.5 million newly issued shares of Arvinas common stock, priced at a 30% premium to the 30-day volume weighted average price on July 20, 2021. This represents an equity ownership stake by Pfizer of approximately 7%. Arvinas is also eligible to receive up to $400 million in approval milestones and up to $1 billion in commercial milestones, in addition to sharing profits on ARV-471 worldwide. Arvinas and Pfizer will jointly develop ARV-471 through a robust clinical program designed to position ARV-471 as an endocrine backbone therapy of choice across the breast cancer treatment paradigm, from the adjuvant setting through late-line metastatic disease.