The trial involved 1,250 women with early breast cancer. Credit: National Cancer Institute on Unsplash.

Pfizer has said that the Phase III PENELOPE-B clinical trial of Ibrance (palbociclib) failed to meet the primary endpoint of improvement in invasive disease-free survival (iDFS) in early breast cancer patients (eBC).

Backed by the German Breast Group (GBG), the trial involved 1,250 women suffering from hormone receptor-positive (HR+), human epidermal growth factor-negative (HER2-) eBC with residual invasive disease after completing treatment with neoadjuvant chemotherapy.

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Ibrance is an oral cyclin-dependent kinases (CDKs) 4/6 inhibitor. CDKs 4 and 6 modulate the cell cycle that induces cellular progression.

The randomised, double-blind, placebo-controlled Phase III trial evaluated one year of palbociclib versus placebo. Both arms were also given at least five years of standard adjuvant endocrine therapy.

The global study, conducted at over 190 sites in 12 countries, started enrolling patients in November 2013 and completed enrolment on 31 December 2017.

Participants scored three or higher on the clinical-pathologic stage – oestrogen/grade (CPS-EG), a risk assessment tool that merges clinical stage prior to neoadjuvant therapy, pathological stage following neoadjuvant therapy, grading and oestrogen-receptor status.

Though PENELOPE-B did not reach the primary endpoint, Pfizer did not report any unexpected safety signals from the trial.

Pfizer Global Product Development Oncology chief development officer Chris Boshoff said: “This is the first randomised Phase III 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.”

Ibrance holds approval to treat postmenopausal women or men with HR+, HER2- advanced or metastatic breast cancer when used with an aromatase inhibitor as initial endocrine based treatment.

The drug can also be given with fulvestrant to patients who experience disease progression after endocrine therapy.

In February this year, Pfizer and Astellas Pharma reported positive results from the Phase III PROSPER trial of Xtandi (enzalutamide) in patients with non-metastatic castration-resistant prostate cancer (nmCRPC).