A completed Pfizer-sponsored Phase 2 randomized trial assessed the CDK inhibitor PF-07220060 combined with letrozole versus letrozole monotherapy as short-course neoadjuvant therapy in postmenopausal women with HR+/HER2− breast cancer. The 14-day interventional window incorporated mandatory Day 14 tumor biopsy to evaluate pharmacodynamic and safety endpoints.
Pfizer has completed a multicenter, open-label, randomized Phase 2 trial (NCT06465368) investigating PF-07220060—an investigational oral CDK inhibitor—in combination with the aromatase inhibitor letrozole as neoadjuvant therapy in postmenopausal women aged 18 years or older with confirmed hormone receptor-positive, HER2-negative breast cancer. The comparator arm received letrozole alone. Notably, all enrolled participants were treatment-naive at study entry.
The trial employed a compressed 14-day treatment window, during which PF-07220060 was administered orally twice daily and letrozole once daily. This short neoadjuvant window design is consistent with a presurgical pharmacodynamic window-of-opportunity paradigm, allowing tumor tissue sampling before and after drug exposure. A mandatory biopsy on Day 14 was required for all participants, enabling direct assessment of on-target biological activity within the tumor microenvironment.
Eligibility was restricted to postmenopausal women—whether naturally or surgically postmenopausal—with histologically confirmed HR+/HER2− disease who had not received prior anticancer therapy. Safety assessments, including serial laboratory evaluations and clinical interviews, were conducted throughout the study period, with a follow-up visit approximately 28 days after the final dose.
Full efficacy and safety results from this completed trial have not yet been publicly disclosed. The short treatment duration and window-of-opportunity design limit direct extrapolation to standard neoadjuvant or adjuvant outcomes; however, biomarker data from Day 14 biopsies may inform dose selection and mechanistic rationale for future Phase 3 development of PF-07220060 in HR+/HER2− breast cancer.
Key points
- PF-07220060, an investigational oral CDK inhibitor, was evaluated in combination with letrozole versus letrozole alone in a completed Phase 2 neoadjuvant window-of-opportunity trial.
- Enrollment was limited to treatment-naive postmenopausal women with HR+/HER2− breast cancer.
- Both agents were administered orally over a 14-day presurgical window; PF-07220060 was dosed twice daily and letrozole once daily.
- Mandatory Day 14 tumor biopsies were obtained from all participants to assess pharmacodynamic endpoints.
- Full trial results have not yet been publicly reported; findings may guide dose optimization and Phase 3 planning.
Why it matters
HR+/HER2− breast cancer represents the most prevalent breast cancer subtype, and CDK inhibition combined with endocrine therapy has become a cornerstone of advanced disease management; neoadjuvant window trials like this one provide critical early biological evidence to support or refine the development of novel CDK inhibitors such as PF-07220060 in earlier disease settings.