The German Breast Group (GBG) and Pfizer announced that the collaborative Phase 3 PENELOPE-B trial did not meet the primary endpoint of improved invasive disease-free survival (iDFS) in women with hormone receptor-positive (HR+), human epidermal growth factor-negative (HER2-) early breast cancer (eBC) who have residual invasive disease after completing neoadjuvant chemotherapy. No unexpected safety signals were observed.

“Reducing the risk of disease recurrence in patients who have residual disease after neoadjuvant chemotherapy is a complex clinical challenge. This unique trial was made possible through the collaboration and support from all the research partners involved. Despite this outcome, we believe that key learnings will emerge from the large number of biomarkers being analysed from collected tumour tissue, which will help inform future breast cancer research,” said Professor Sibylle Loibl, Chair of GBG.

“This is the first randomised Phase 3 study to establish mature iDFS results for a CDK4/6 inhibitor as part of the adjuvant treatment for early breast cancer. While we are disappointed with this result, we look forward to continuing to work with our research partners to understand subgroup data and how these could inform the development of our next-generation CDK inhibitors in early breast cancer,” said Chris Boshoff, Chief Development Officer, Oncology, Pfizer Global Product Development.

Detailed findings from PENELOPE-B will be presented at an upcoming medical congress.