Real-World Tumor Response of Palbociclib in Combination With an Aromatase Inhibitor as First-Line Therapy in Pre/Perimenopausal Women With Metastatic Breast Cancer.

ABSTRACT

BACKGROUND: Limited real-world data exist regarding the efficacy of palbociclib in combination with endocrine therapy in pre/perimenopausal women with metastatic breast cancer. OBJECTIVE: We aimed to compare real-world tumor responses among pre/perimenopausal women who initiated palbociclib plus an aromatase inhibitor (AI) or AI monotherapy as first-line treatment for hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer. METHODS: This retrospective observational cohort study (NCT05012644) used electronic health record data from The US Oncology Network. Tumor responses were determined based on treating clinicians' assessments of radiologic evidence for changes in disease burden. Normalized inverse probability treatment weighting was used to balance baseline characteristics between treatment cohorts. RESULTS: Of 196 pre/perimenopausal women, 116 and 80 were in the palbociclib plus AI cohort and AI cohort, respectively. Real-world response rates (complete or partial response) were 52.1% and 46.2%, respectively (odds ratio, 1.27 [95% confidence interval 0.72‒2.24]). Among patients with one or more tumor assessments on treatment, real-world response rates were 60.0% in the palbociclib plus AI cohort (n = 103) and 49.9% in the AI cohort (n = 71; odds ratio, 1.51 [95% confidence interval 0.82‒2.77]). CONCLUSIONS: This real-world analysis suggests that pre/perimenopausal patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer appear more likely to respond to palbociclib plus AI versus AI alone as first-line therapy, which may support the combination as a standard-of-care treatment for this patient population.

Palbociclib (Ibrance®) is a medicine for patients with metastatic breast cancer (MBC). Metastatic means that the cancer has spread to other places in the body. Patients take palbociclib with hormone therapy, such as an aromatase inhibitor (AI). Palbociclib plus an AI is a treatment for a type of MBC called HR+/HER2‒ MBC. HR+/HER2‒ stands for hormone receptor positive, human epidermal growth factor receptor 2 negative. Researchers wanted to observe responses to treatment in routine clinical practice among women with HR+/HER2­ MBC who had not reached menopause. A response is if a tumor shrinks or disappears after treatment. This study used healthcare information reported in electronic medical records of patients seen by doctors in The US Oncology Network. This study included 196 women with HR+/HER2­ MBC who had not reached menopause and had not received prior treatment for MBC. A total of 116 women received palbociclib plus an AI, and 80 women received an AI alone. Researchers used standard statistical approaches to balance baseline characteristics between the two treatment groups. These adjustments made the groups more similar so that researchers could compare treatment responses. Sixty percent of patients who took palbociclib plus an AI responded, compared with 50% of patients who took an AI alone. These results suggest that palbociclib plus an AI may benefit women with HR+/HER2‒ MBC who have not reached menopause.