Pfizer has a lofty goal for the CDK4 inhibitor atirmociclib, the New York pharma’s answer to Ibrance’s loss of patent protection next year. In 2025, Ibrance led Pfizer’s oncology portfolio with $1.04 billion in sales.
The drug that could one day replace Ibrance as Pfizer’s leading breast cancer offering improved progression-free survival, with a 40% reduction in the risk of disease progression or death during a mid-stage trial.
The positive results come as sales of Ibrance are already starting to decline, with a patent cliff looming in 2027. Last year, the CDK4/6 inhibitor brought in $1.04 billion, a 5% dip from 2024.
Pfizer on Tuesday revealed results from the Phase 2 FOURLIGHT-1 study of Ibrance’s potential successor, atirmociclib. The CDK4 inhibitor was tested in patients with HR-positive, HER2-negative (HR+/HER2-) advanced or metastatic breast cancer who had experienced progression after previous treatment with a CDK4/6 inhibitor. Atirmociclib was paired with AstraZeneca’s Faslodex or Novartis’ Afinitor plus Pfizer’s older medicine Aromasin.
Atirmociclib met the main goal of the trial, which was to improve progression-free survival. This result was consistent across different subgroups, including performance status, menopausal status, presence of visceral disease, duration of prior treatment and which CDK4/6 inhibitor had previously been received.
Pfizer said that overall survival, a key secondary endpoint, was not mature as of the data cutoff.
Atirmociclib also showcased a safety profile that Pfizer described as manageable, with 6.4% of patients discontinuing due to treatment-emergent adverse events. The profile was consistent with previous studies, Pfizer said.
Pfizer has a lofty goal for atirmociclib as the heir apparent to Ibrance. Pfizer is pushing atirmociclib for earlier or first-line cancer treatment in hopes of chipping off more of the breast cancer market that was once held by Ibrance.
Patients with first line HR+/HER2- disease represent about 65% to 70% of the entire breast cancer population, BMO Capital Markets wrote in a note last year as Pfizer touted its oncology portfolio. Pfizer specifically has been trumpeting atirmociclib as potentially having a better safety profile than other agents.
