Treatment and Monitoring Patterns Among Premenopausal Women with HR+/HER2-Advanced Breast Cancer

Introduction: Premenopausal women with hormone receptor positive (HR+) and human epidermal growth factor receptor-2-negative (HER2-) advanced breast cancer (aBC) often present with aggressive tumor types that lead to poor prognosis, high rates of recurrence, and mortality. Although clinical guidelines provide evidence-based recommendations for optimal treatment and monitoring, there is a dearth of information regarding treatment and monitoring patterns in clinical practice. In this study, we describe treatment and monitoring patterns among premenopausal women with HR+/HER2- aBC in real-world practice. Methods: A large US claims database was used to describe treatment patterns for patients in first, second, and third lines of therapy. Treatment monitoring included complete blood count (CBC), liver function test (LFT), and electrocardiogram (EKG) monitoring, described for the first three lines of therapy, and separately for patients receiving endocrine monotherapy (ET) and chemotherapy. Results: Among 3203 patients, chemotherapy was the most common treatment used in firstline (63.6%) and second-line therapy (66.9%). ET was used in 34.4, 30.1, and 73.6% of patients in first, second, and third lines of therapy, respectively. The two most common treatment sequences were a single line of ET (27.3%), and two consecutive lines of chemotherapy followed by a line of ET (19.3%). Patients receiving chemotherapy were monitored with CBC on average more than two times per month, and for LFT one to two times per month. Patients receiving ET were monitored with CBC and LFT on average once every 2-3 months. Overall, approximately 20% of patients were monitored with an EKG at some point during each line of therapy. Conclusion: A considerable proportion of premenopausal women with aBC received first- and second-line chemotherapy, which appears inconsistent with current clinical guidelines. The observed treatment heterogeneity points to a lack real-world consensus on the management of premenopausal women with HR+/HER2- aBC.