Pfizer announced on Mar. 17 that its investigational drug atirmociclib, which could succeed Ibrance as the company’s main breast cancer therapy, reduced the risk of disease progression or death by 40% in a mid-stage clinical trial.
The findings are significant as sales of Ibrance have begun to decline ahead of an expected patent expiration in 2027. Last year, Ibrance generated $1.04 billion in revenue, marking a 5% decrease from 2024.
According to Pfizer, the Phase 2 FOURLIGHT-1 study evaluated atirmociclib—a CDK4 inhibitor—in patients with HR-positive, HER2-negative advanced or metastatic breast cancer who had previously progressed after treatment with a CDK4/6 inhibitor. The drug was administered alongside AstraZeneca’s Faslodex or Novartis’ Afinitor plus Pfizer’s Aromasin. Atirmociclib achieved the primary endpoint of improving progression-free survival across various patient subgroups, including those defined by performance status, menopausal status, presence of visceral disease, duration of prior treatment, and type of previous CDK4/6 inhibitor received.
Pfizer said that data on overall survival—a key secondary measure—were not yet mature at the time of analysis. The company also reported that atirmociclib demonstrated a manageable safety profile consistent with earlier studies; 6.4% of patients discontinued due to adverse events related to treatment.
Pfizer is positioning atirmociclib for use in earlier lines or first-line settings for HR-positive, HER2-negative breast cancer. According to BMO Capital Markets last year, patients with first-line HR+/HER2- disease account for about 65% to 70% of all breast cancer cases as Pfizer continues to promote its oncology portfolio.
