Balixafortide Does Not Meet Co-Primary Endpoint of Overall Response Rate in Patients with Advanced HER2 Negative Breast Cancer


The clinical benefit rate was observed in 16.7% of patients in the balixafortide arm and in 19.6% of patients in the eribulin monotherapy arm.

In updated data from the phase III FORTRESS study of balixafortide in patients with advanced human epidermal growth factor receptor 2 (HER2) negative breast cancer, investigators said the trial failed to meet the co-primary endpoint of objective response rate (ORR).

The FORTRESS study is an international, multicenter, randomized open-label trial which is investigating the efficacy, safety, and tolerability of intravenous balixafortide in combination with eribulin compared to eribulin alone in patients with HER2 negative, locally recurrent or metastatic breast cancer. The study randomized 432 patients, at least 344 of whom were receiving third or subsequent line therapy and 88 of whom were receiving second line therapy.

Balixafortide is a potent, specific, and highly selective antagonist of the chemokine receptor CXCR4, which regulates the trafficking and homing of both cancer cells and cells from the patient’s immune system, according to Polyphor, the biopharmaceutical company that initiated the study.

At the primary analysis of the FORTRESS study, investigators found no improvement in the ORR for patients receiving balixafortide plus eribulin compared with eribulin alone (13% versus 13.7%, respectively) in the third line and later population. The clinical benefit rate, which indicates a stable disease or any confirmed response for a duration of at least 6 months, was observed in 16.7% of patients in the balixafortide arm and in 19.6% of patients in the eribulin monotherapy arm.

The study did confirm the positive safety and tolerability profile of balixafortide found in the previously reported phase 1b study. According to Polyphor, investigators will continue to analyze the data and will decide about the future of the study in July.

“Given the high unmet medical need for patients with HER2 negative breast cancer in a late stage of the disease, we are disappointed that the FORTRESS study did not meet its coprimary endpoint,” said Gokhan Batur, CEO of Polyphor, in a press release.


Polyphor Provides Update on the Phase III FORTRESS Study of Balixafortide in Patients With Advanced HER2 Negative Breast Cancer. News release. Global Newswire. June 28, 2021. Accessed June 30, 2021.

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