Dr Kalinsky on Efficacy Data From SERENA-6 in ER+/HER2– Advanced Breast Cancer

“We saw that early switching [to camizestrant from an aromatase inhibitor] improved PFS in patients who did not have radiographic disease progression.”

Kevin Kalinsky, MD, MS, FASCO, director of the Glenn Family Breast Center at Winship Cancer Institute of Emory University and professor and director in the Division of Medical Oncology of the Department of Hematology and Medical Oncology at Emory University School of Medicine, discussed efficacy data from the phase 3 SERENA-6 study (NCT04964934) of camizestrant in combination with a CDK4/6 inhibitor in patients with estrogen receptor–positive, HER2-negative advanced breast cancer.

Data presented during the 2025 ASCO Annual Meeting revealed that patients who switched from an aromatase inhibitor (AI) to camizestrant plus a CDK4/6 inhibitor following the detection of an ESR1 mutation (n = 157) experienced a median progression-free survival (PFS) of 16.0 months (95% CI, 12.7-18.2) per investigator assessment. Comparatively, patients who remained on an AI plus a CDK4/6 inhibitor (n = 158) achieved a median PFS of 9.2 months (95% CI, 7.2-9.5).

The adjusted HR for PFS was 0.44 (95% CI, 0.31-0.60; P < .00001) in favor of the camizestrant arm. The 12- and 24-month PFS rates in the camizestrant were 60.7% and 29.7%, respectively. These respective rates were 33.4% and 5.4% in the control arm.

In terms of second PFS (PFS2), which was a key secondary end point of SERENA-6, the adjusted HR was 0.52 (95% CI, 0.33-0.81; P = .0038). The study authors noted that the interim analysis threshold for PFS2 significance was P = .0001.

ESR1 mutations are adaptive resistance mechanisms which happen following treatment with an AI, Kalinsky explained. In SERENA-6, it was notable that early switching to camizestrant improved the median PFS despite these patients not showing evidence of radiographic disease progression, he added. The median time from initiation of treatment with an AI plus a CDK4/6 inhibitor to random assignment in the investigational arm was 23 months (range, 7-96), which is important to consider when interpreting the data from SERENA-6, Kalinsky said. Investigators are looking forward to more mature data from the study, including overall survival and detailed PFS2 findings, Kalinsky concluded.

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