The German Breast Group (GBG) and Pfizer Inc. today 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.

PENELOPE-B is a randomized, double-blind, placebo-controlled Phase 3 study comparing one year of palbociclib plus at least five years of standard adjuvant endocrine therapy to placebo plus at least five years of standard adjuvant endocrine therapy. The trial is sponsored by the GBG as part of a clinical research collaboration with Pfizer and other study groups.
“Reducing the risk of disease recurrence in patients who have residual disease after neoadjuvant chemotherapy is a complex clinical challenge,” said Professor Sibylle Loibl, Chair of GBG. “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 analyzed from collected tumor tissue, which will help inform future breast cancer research.”

"This is the first randomized 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, M.D., Ph.D., Chief Development Officer, Oncology, Pfizer Global Product Development. “We are proud of the transformative impact IBRANCE has had on the treatment of HR+, HER2- metastatic breast cancer - a vastly different treatment setting than early breast cancer. Our commitment to the metastatic patient community is as strong as ever as we continue to generate new data, including the most extensive body of real-world evidence for a CDK 4/6 inhibitor.”