New data on Pfizer’s new breast cancer candidate palbociclib show the drug can extend progression-free survival (PFS) when added to standard treatment.
The phase II trial showed that palbociclib doubled PFS to a little over 20 months when given alongside Novartis’ Femara (letrozole) in patients with oestrogen receptor-positive, HER2-negative advanced breast cancer.
The drug also showed a trend towards improved overall survival (OS) compared to Femara alone – at 37.5 months versus 33.3 months – but at present this is not a statistically significant difference.
Less than a third of the patients in the trial had died by the time the latest analysis was carried out, so the difference could slide into significance over time, according to lead investigator Richard Finn of the University of California, Los Angeles, who presented the data yesterday at the American Association of Cancer Research (AACR) meeting in San Diego.
Palbociclib is a first-in-class cyclin-dependent kinase (CDK) 4 and 6 inhibitor that has been granted breakthrough status by the US FDA, and could be a useful new drug for the 60 per cent of breast cancer patients that have that receptor profile.
Pfizer has suggested in the past it may be possible to progress with a filing for palbociclib on the strength of the phase II data – subject of course to negotiation and agreement with regulatory authorities – although analysts have said this may be challenging without solid data on overall survival rates.
Pfizer recently started two phase III studies of palbociclib in advanced breast cancer patients, as well as a third pivotal study in patients with early breast cancer at a high-risk of recurrence.
“The potential impact of this study could be huge,” said Dennis Slamon of UCLA, who was involved in the preclinical work on the drug.
“The current data are as exciting as the initial studies we were involved in when testing trastuzumab [Roche’s mega blockbuster Herceptin] for HER2-positive breast cancers,” he added.
Palbociclib has been tipped to achieve sales of $3bn-plus a year if approved and is considered to be one of the brightest hopes in Pfizer’s near-term pipeline.