Dr. Chavez Mac Gregor on Key Results From SWOG S1207 in HR+/HER2- Breast Cancer

Mariana Chavez Mac Gregor, MD, MSC, associate professor, Department of Health Services Research, Division of Cancer Prevention and Population Sciences, The University of Texas MD Anderson Cancer Center, discusses key efficacy and safety data from the phase 3 SWOG S1207 trial (NCT01674140) of everolimus (Afinitor) in hormone receptor (HR)–positive, HER2-negative breast cancer.

This randomized, placebo-controlled trial investigated the role of the addition of the mTOR-inhibitor everolimus plus standard adjuvant endocrine therapy in high-risk patients, Chavez Mac Gregor begins. Patients were randomly assigned 1:1 to either the investigator’s choice of adjuvant endocrine therapy plus 1 year of everolimus or placebo. The trial’s primary end point was invasive disease-free survival (IDFS), with secondary end points including overall survival (OS) and safety. Subset analyses included a preplanned evaluation according to risk group and exploratory analyses of menopausal status and age.

Final analysis by risk group revealed that everolimus elicited no improvement in survival outcomes among postmenopausal patients, Chavez Mac Gregor states. However, an exploratory analysis of 581 premenopausal patients did show a statistically significant increase in both IDFS and OS, Chavez Mac Gregor says. Despite the negative outcome of this study, these data were thought-provoking and hypothesis-generating, she emphasizes.

Safety data showed that patients treated with everolimus also experienced a higher rate of grade 3 and 4 adverse events (AEs) compared with patients in the control group, Chavez Mac Gregor continues. Moreover, the treatment discontinuation rate was higher in the experimental arm due to treatment-related adverse events, she states. These results signify the need for improved understanding of the drug’s toxicity profile, tolerability, and AE management in this patient population, Chavez Mac Gregor explains. Future research should aim to address the low completion rate and high toxicity associated with everolimus.