Global pharma giant Pfizer has said that its experimental cancer drug atirmociclib delivered a significant boost in delaying disease progression in patients with advanced breast cancer, marking a potential breakthrough for a hard-to-treat population.
In the mid-stage FOURLIGHT-1 trial, patients receiving atirmociclib alongside fulvestrant saw a statistically significant improvement in progression-free survival compared to those on standard therapies. The study hit its main goal, with results showing a 40% reduction in the risk of disease progression or death.
The benefit held steady across all patient groups studied — including those with more aggressive disease and those whose cancer had quickly worsened after earlier treatment with CDK4/6 inhibitors, the current standard of care.
“These results are especially encouraging given that the FOURLIGHT-1 study enrolled patients whose disease had progressed soon after prior CDK4/6 inhibitor therapy, a difficult-to-treat population,” said Jeff Legos, Chief Oncology Officer, Pfizer.
“The strength of these data reinforces our confidence that atirmociclib may meaningfully differentiate from the CDK4/6 inhibitor class, the standard-of-care backbone in HR-positive breast cancer, with the potential for improved efficacy and tolerability. We are continuing to accelerate development of this next-generation cell cycle inhibitor in earlier lines of therapy where it may offer even greater benefit for patients.”
The drug also showed a manageable safety profile, with just 6.4% of patients stopping treatment due to side effects. No new safety concerns emerged.
While overall survival data is still early, with only about one-fifth of participants experiencing events so far, the results mark the first randomized Phase 2 evidence for atirmociclib — a potential first-in-class CDK4 inhibitor.
The FOURLIGHT-1 study enrolled 264 patients across 14 countries whose cancer had already progressed after prior CDK4/6 inhibitor treatment. More than 90% began the new therapy within three months of their last regimen.
Pfizer said it is now pushing ahead with late-stage development, including an ongoing Phase 3 trial in first-line metastatic breast cancer and additional studies in earlier-stage disease, where the company believes the drug could have the greatest impact.
