The German Breast Group (GBG) and Pfizer announced that its phase 3 trial of palbociclib did not meet the primary end point for the treatment of women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) early breast cancer who have residual invasive disease after completing neoadjuvant chemotherapy.

The randomized, double-blind, placebo-controlled PENELOPE-B trial compared 1 year of palbociclib to placebo plus at least 5 years of standard adjuvant endocrine therapy in 1250 women with HR+, HER2- early breast cancer at high risk of recurrence who have residual invasive disease after completing neoadjuvant chemotherapy. 

The trial included patients who had a score of 3 or higher (or 2 if lymph node metastases were present at the time of surgery) on the clinical-pathologic stage – estrogen/grade (CPS-EG). Patients were randomized to receive placebo or palbociclib 125mg orally once daily on days 1 to 21, followed by 7 days off treatment in a 28-day cycle for 13 cycles.

Results showed that palbociclib did not meet the primary end point of improved invasive disease free survival (iDFS), defined according to Hudis (J Clin Oncol 2007) as the time period between randomization and first event. Detailed study findings will be presented at an upcoming medical congress.

“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.”

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Palbociclib, a kinase inhibitor, is marketed under the trade name Ibrance® and is currently indicated for the treatment of HR+, HER2- advanced or metastatic breast cancer in combination with an aromatase inhibitor as initial endocrine based therapy in postmenopausal women or in men; or with fulvestrant in patients with disease progression following endocrine therapy.

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PENELOPE-B trial of Ibrance® (palbociclib) in early breast cancer did not meet primary endpoint. [press release]. New York, NY: Pfizer; October 9, 2020.