Patients with HR+/ HER2+ advanced breast cancer who received ribociclib, trastuzumab, and letrozole as first-line therapy had a progression-free survival (PFS) of 30.4 months, according to recent research from the 2025 ASCO Annual Meeting. 

In a multicenter, single-arm, prospective trial, researchers from South Korea enrolled patients in a phase 1b/2 trial who had HR-positive/ HER2-negative+ advanced breast cancer and no history of systemic therapy who received once-daily ribociclib (600 mg), once-daily letrozole (2.5 mg), and trastuzumab (6 mg/kg) every 3 weeks. 

Overall, 13 patients were enrolled in the phase 1b portion of the trial, and 77 patients were enrolled in the phase 2 portion of the trial.  

Researchers evaluated PFS as a primary endpoint, with secondary endpoints of overall survival, objective response rate (ORR), duration of response (DOR), and safety. 

Patients in the phase 2 portion of the trial were median 61 years old, 18.2% were premenopausal, 66.2% had a HER2 immunohistochemistry score of 3+, 66.2% had visceral metastases, and 64.9% had recurrent disease. 

Researchers found patients had a median PFS of 30.4 months at median 15.8 months of follow-up.  

“Ribociclib, trastuzumab, and letrozole as first-line therapy in HR+/HER2+ [advanced breast cancer] demonstrated a median PFS of 30.4 months with a manageable safety profile, supporting its potential as a chemotherapy-free option,” 

- Joohyuk Sohn, MD, PhD, of the division of medical oncology, at Yonsei Cancer Center in Seoul, and fellow authors wrote. 

Sohn and colleagues also found an ORR of 61.1% and a DOR of 11.8 months. 

Patients in the study most commonly experienced neutropenia, pruritus, and nausea as adverse events. There was one death in the study, which was due to aortic aneurysm. 

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References:  
https://meetings.asco.org/abstracts-presentations/244389 

https://clinicaltrials.gov/study/NCT03913234 

Disclosures: Some authors declared financial ties to drugmakers. See full study for details. 

Photo Credit: Getty Images 

By Jeff Craven