Pfizer’s Ibrance breast cancer drug combo fails to improve OS in phase 3 trial

The study assessed Ibrance in combination with fulvestrant against placebo plus fulvestrant in women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer whose disease has progressed after prior endocrine therapy.

Ibrance is an oral inhibitor of CDKs 4 and 6, which are crucial regulators of the cell cycle that activate cellular progression.

The phase 3 trial showed a positive trend in the hazard ratio supporting the Ibrance combination, while this trend did not achieve statistical significance.

Pfizer said that OS is a secondary endpoint of the Paloma-3 trial, buy its design was not optimized to detect a statistically significant difference in OS

Pfizer global product development chief development officer Dr Mace Rothenberg said: “While the difference in overall survival 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 previously demonstrated in this trial.”

“Ibrance in combination with endocrine therapy has transformed the treatment landscape for patients with HR+, HER2- metastatic breast cancer.”

The Paloma-3 trial, which achieved its primary endpoint of progression-free survival (PFS) at interim analysis, showed a statistically significant and clinically meaningful improvement in PFS for Ibrance plus fulvestrant compared against placebo plus fulvestrant.

Based on the PFS demonstrated in Paloma-3 trial, the Ibrance in combination with fulvestrant secured approval in over 80 countries across the globe.

In the US, Ibrance secured approval 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 fulvestrant in women with disease progression following endocrine therapy.