A Pfizer drug for the treatment of breast cancer, containing the active ingredient atirmociclib and currently in the second stage of clinical trials, has been shown to reduce the risk of disease progression or death by 40%, the company announced in a press release. The release specified that the drug’s effect was studied in combination with fulvestrant.
More than 90% of patients began treatment with atirmociclib within three months of their last therapy with a CDK4/6 inhibitor.
“These data reinforce our confidence that atirmociclib could be meaningfully differentiated from the class of CDK4/6 inhibitors, the standard backbone of care in HR-positive breast cancer, with the potential to improve upon both efficacy and tolerability,” said Jeff Legos, Senior Vice President & Head of Oncology Development at Pfizer.
In the study, atirmociclib demonstrated a manageable safety profile and was well-tolerated, although 6.4% of patients discontinued the drug due to adverse events. These results support Pfizer’s strategy of advancing atirmociclib in first-line and early-stage disease settings, where sustained endocrine control could have the greatest impact.
In November 2025, the U.S. Food and Drug Administration (FDA) approved the combination of MSD’s Keytruda (pembrolizumab) and Padcev (enfortumab vedotin), from Pfizer and Astellas, for the treatment of bladder cancer.
