Phase III study shows Pfizer's Ibrance more than doubles PFS in advanced breast cancer

Pfizer detailed results from the Phase III PALOMA-3 study to be presented at the ASCO annual meeting demonstrating that its oral CDK 4/6 inhibitor Ibrance (palbociclib), in combination with AstraZeneca's Faslodex (fulvestrant), significantly prolonged progression-free survival (PFS) in certain women with metastatic breast cancer, compared with Faslodex alone. "We now have information that indicates that Ibrance can substantially delay the time to tumour progression when used in the first-line or second-line setting," remarked Mace Rothenberg, chief medical officer for Pfizer's oncology unit.

In April, the drugmaker announced that the trial, whose results were simultaneously published in the NEJM, was stopped early after having met its primary endpoint of improving PFS. Pfizer said that based on the data, it is in "discussions with global regulatory authorities to determine next steps to potentially make [Ibrance] available for women with HR+, HER2- metastatic breast cancer whose disease has progressed following endocrine therapy."

The study randomised 521 pre/perimenopausal and postmenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer whose disease had progressed during or after endocrine therapy to receive Faslodex in combination with Ibrance or placebo. An interim analysis showed that PFS was 9.2 months in patients given Ibrance plus Fasodex, versus 3.8 months for those who received Faslodex plus placebo.

According to Pfizer, adverse events observed with the combination treatment were consistent with the drugs' respective safety profiles. In the Ibrance plus Faslodex group, the most common adverse events were neutropenia, leukopenia, fatigue and nausea, while the rate of febrile neutropenia was 0.6 percent in both study arms and serious adverse events were balanced across the two groups. The company added that discontinuation rates due to adverse events were 2.6 percent in the Ibrance plus Faslodex group and 1.7 percent in the Faslodex plus placebo group.

Commenting on the results, ASCO spokesperson Don Dizon said "this represents a new standard of care option...we await follow-up for overall survival."

In February, Ibrance was granted accelerated approval by the FDA, in combination with Novartis' Femara (letrozole), as a first-line treatment for women with advanced or metastatic oestrogen receptor-positive, HER2-negative breast cancer. As previously disclosed, Pfizer said it intends to file for marketing approval of Ibrance with the European Medicines Agency in the second half of this year. Analysts predict that the product could generate peak annual sales of more than $5 billion.

For related analysis, read ViewPoints: Pfizer's big new drug launch likely to get stronger and Analyst Notes: Ibrance launch will change the way HER2-negative/HR-positive breast cancer is treated, argue KOLs.

See also Breast Cancer: KOL Insight; New CDK inhibitors and PARP inhibitors will transform treatment paradigms.

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