Oops. Pfizer’s CDK 4/6 blockbuster Ibrance flunks the OS mark for breast cancer

Just weeks after Novartis $NVS set out to burnish its prospects in breast cancer with promising progressive-free survival numbers for Kisqali and fulvestrant in treating patients with HR+/HER2- advanced breast cancer, rival Pfizer $PFE has some confessing to do today about its blockbuster market-leading duo using Ibrance.

Mace Rothenberg

Pfizer’s combo using fulvestrant failed to achieve statistical significance for overall survival in PALOMA-3, which will likely give the competition a serious leg up as they try to play catch-up. Ibrance is one of three key CDK 4/6 drugs on the market, including Kisqali and Eli Lilly’s $LLY Verzenio.

Investigators studied patients whose disease had progressed after endocrine therapy. The study had hit on progression-free survival three years ago, setting up a landmark approval in early 2016 that helped deliver $3.1 billion to Pfizer in 2017.

The pharma giant worked at downplaying the critical OS failure, noting that there was a trend in its favor — virtually meaningless — and that the study wasn’t actually powered to determine overall survival. 

Besides, says the principal investigator, actually nailing down positive OS in this setting is extremely difficult.

“The duration of the survival in hormone receptor-positive metastatic breast cancer patients, and the potential for subsequent therapies to confound overall survival outcomes, make demonstrating statistically significant improvement in overall survival extremely difficult,” said Nicholas Turner, professor of molecular oncology at The Institute of Cancer Research.

“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. We are encouraged by these results, which build on the compelling clinical benefit delivered by Ibrance,” said Mace Rothenberg, who runs the oncology R&D group at Pfizer.

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Skyhawk Therapeutics Waltham, MA
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