Ibrance is an oral inhibitor of CDKs 4 and 6, which are important regulators of the cell cycle that trigger cellular progression.
The study met its primary endpoint demonstrating improvement in progression-free survival (PFS) for the combination compared with letrozole plus placebo in post-menopausal women with oestrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+, HER2-) advanced or metastatic breast cancer who had not received previous systemic treatment for their advanced disease.
Pfizer said the data will support further planned regulatory submissions globally and a request for conversion of the accelerated approval for Ibrance to regular approval in the US.
The US Food and Drug Administration initially approved Ibrance in February 2015 based on the results of Paloma-1.
Pfizer Oncology chief medical officer & senior vice president, Global Product Development, Oncology Mace Rothenberg said: "These results provide confirmatory evidence for Paloma-1 and will be used to support regulatory submissions around the world, including a request for conversion of Ibrance from accelerated to full approval in the United States.
"We look forward to sharing the detailed results of Paloma-2 with the oncology community and advancing our discussions with regulatory authorities."
Ibrance also is approved in eight countries outside of the US. Pfizer has filed a Marketing Authorization Application with the European Medicines Agency for the drug in combination with endocrine therapy to treat HR+, HER2- advanced or metastatic breast cancer.
Image: Pfizer World headquarters in New York City. Photo: courtesy of Norbert Nagel, Mörfelden-Walldorf, Germany.