Pfizer's Ibrance fails to significantly extend survival in Phase III breast cancer study

Pfizer on Monday unveiled data from the Phase III PALOMA-3 trial showing that its oral CDK 4/6 inhibitor Ibrance (palbociclib) in combination with AstraZeneca's Faslodex (fulvestrant) failed to significantly prolong overall survival (OS), compared to Faslodex alone, in women with hormone receptor-positive (HR+), HER2-negative metastatic breast cancer who experienced disease progression following previous endocrine therapy. Mace Rothenberg, chief development officer of oncology for Pfizer's global product development unit, remarked "while the difference in [OS] narrowly missed the threshold for statistical significance – a high bar for any trial in this patient population – it is similar, in absolute terms, to the improvement in median progression-free survival (PFS) previously demonstrated in this trial." 

Pfizer noted that the data nonetheless revealed a "positive trend" in favour of the combination in OS, a secondary endpoint of PALOMA-3. Principal investigator Nicholas Turner, who said the findings were still "encouraging for physicians and patients," suggested that "the duration of survival in HR+ metastatic breast cancer patients, and the potential for subsequent therapies to confound OS outcomes, make demonstrating statistically significant improvement in OS extremely difficult." Detailed study results will be presented at a later research conference. 

FirstWord reports in this therapy area - KOL Insight Breast Cancer: Find out how KOLs expect the market to evolve, which pipeline treatments are most promising, and which clinical trials will shape treatment decisions. Learn more. 

Pfizer unveiled data from the study in 2015 demonstrating that the addition of Ibrance to Faslodex more than doubled the primary endpoint of PFS versus Faslodex alone. PALOMA-3 had been halted early after an assessment by an independent data monitoring committee. 

In the US, Ibrance is already indicated for HR+, HER2-negative advanced or metastatic breast cancer in combination with Faslodex in women with disease progression following endocrine therapy. Last year, the FDA broadened the label for Ibrance to include the combination with an aromatase inhibitor, expanding on its earlier indication in combination with Novartis' Femara (letrozole), as initial endocrine-based therapy in postmenopausal women with HR+, HER2-negative advanced or metastatic breast cancer.

Sales of Ibrance jumped 37 percent in the first quarter to $933 million. 

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