While under competitive pressure from Novartis and Eli Lilly, Pfizer can tally up a unique trial win for its Ibrance in a niche breast cancer population.
Although CDK4/6 inhibitors such as Ibrance are well-established treatments for HR-positive, HER2-negative breast cancer, a phase 3 trial sponsored by the cancer research organization Alliance Foundation Trials has now found that the Pfizer drug can provide benefit in HR-positive, HER2-positive tumors as well.
The addition of Ibrance to current standard-of-care anti-HER2 and endocrine therapy in HR+/HER2+ breast cancer patients who’ve responded to induction chemotherapy reduced the risk of progression or death by 26% compared with HER2 and endocrine therapy alone.
The results came from a phase 3 trial coded PATINA, which is the first large phase 3 trial to show the benefit of a CDK4/6 inhibitor in HR+/HER2+ metastatic breast cancer, according to principal investigator Otto Metzger, M.D., from Dana-Farber Cancer Institute.
Measured against the current standard-of-care anti-HER2 and endocrine therapy in the first-line maintenance setting, the Ibrance combo extended patients’ median progression-free survival time by 15.2 months to 44.3 months. The data were released during the 2024 San Antonio Breast Cancer Symposium.
Patient survival data remained immature at the time of the analysis but were trending in favor of the Ibrance arm with a preliminary death-risk reduction figure of 14%. Currently, the estimated five-year survival rates were 74.3% and 69.8% for Ibrance and control, respectively. The analysis was conducted when 119 patients had passed away, while the final overall survival analysis is planned at 247 events.
Pfizer said it plans to share the trial’s results with regulatory authorities.
HR+/HER2+ breast cancer, also known as double-positive breast cancer, constitutes about 10% of all breast cancer cases, whereas about 70% of breast cancers are classified as HR+/HER2- disease.
Lately, Ibrance has been at a disadvantage against competitors Kisqali from Novartis and Verzenio from Eli Lilly after the Pfizer drug missed the overall survival endpoint in the phase 3 PALOMA-2 trial in first-line HR+/HER2- breast cancer and failed two postsurgery adjuvant studies.
In the third quarter, Ibrance’s sales slid 13% year over year to $1.09 billion, whereas Kisqali’s sales jumped 40% to $787 million and Verzenio’s increased by 32% to $1.37 billion.
Despite those trial failures, Ibrance, as the first-to-market CDK4/6 inhibitor, has managed to maintain a sizable market share—thanks partly to doctors’ familiarity with the agent.
Amid the questions about Ibrance’s efficacy, a new real-world study funded by Pfizer has found that the three CDK4/6 inhibitors are not that different when used alongside endocrine therapy as first-line treatment in HR+/HER2- breast cancer.
To conduct the retrospective comparative effectiveness study, researchers gleaned de-identified electronic health records from Flatiron Health in the U.S. Across about 800 sites of care, the study identified 9,146 eligible patients who initiated first-line treatment with a CDK4/6-based combo between February 2015 and November 2023.
Both the unadjusted and baseline characteristics-adjusted overall survival analyses slightly favored the Novartis and Lilly drugs in their respective comparisons with Ibrance, but the differences were not significant, according to the researchers.
In the baseline characteristics-adjusted analysis, Verzenio was linked to a nonsignificant 5% lower risk of death versus Ibrance; Kisqali showed a 2% improvement in that analysis.
As a retrospective database analysis, the study carries the potential flaw for treatment selection bias, the researchers noted. Besides, as Ibrance has been around for much longer, it has longer follow-up periods available compared with the other two meds.