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To examine the real-world incidence and management of select adverse events (AEs) among female patients with hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) metastatic breast cancer (MBC), receiving a cyclin-dependent kinase 4 and 6 (CDK4 and 6) inhibitor (palbociclib, abemaciclib, or ribociclib). This retrospective study analyzed data from the US Oncology Network iKnowMed electronic health record database for 396 patients with an initial MBC diagnosis on/after 1 January 2014 and receipt of first CDK4 and 6 regimen between 1 January 2017 and 31 December 2018. In this descriptive study, the proportion of patients who experienced select AEs and associated dose modifications or discontinuations were reported. The occurrence of select healthcare resource utilization categories was also reported. Median follow-up time was 451, 262, and 355 days for patients in the palbociclib, abemaciclib, and ribociclib cohorts, respectively. The most common AEs were neutropenia (palbociclib, 44.8%; abemaciclib, 10.6%; ribociclib, 36.3%), diarrhea (palbociclib, 8.0%; abemaciclib, 43.0%; ribociclib, 8.8%), and fatigue (palbociclib, 12.9%; abemaciclib, 17.6%; ribociclib, 16.5%). AEs resulted in a treatment hold among 91 (23.0%), a dose reduction among 86 (21.7%), and permanent discontinuation among 48 (12.1%) patients overall. This real-world study provides insight into the occurrence of AEs which varied by CDK4 and 6 inhibitor. Compared to clinical trials, frequencies of AEs were numerically lower but dose reductions due to AEs were numerically higher. It is possible these differences reflect proactive management of AEs on the part of clinicians to help patients remain on therapy. Cyclin-dependent kinase 4 and 6 inhibitors (CDK4 and 6 inhibitors) have changed the landscape for the treatment of metastatic breast cancer (MBC) among patients who are hormone receptor positive (HR+) and human epidermal growth factor receptor 2 negative (HER2−). An understanding of the real-world management of adverse events (AEs) will help optimize treatment strategies. Here, data from the US Oncology Network electronic health record database for 396 HR+, HER2−, MBC patients receiving a CDK4 and 6 inhibitor were examined to describe the proportion of patients who experienced select AEs and the associated outcomes of these AEs. Compared to clinical trials, frequencies of AEs were numerically lower but dose reductions due to AEs were numerically higher. It is possible that these differences reflect a proactive management of AEs on the part of clinicians to help patients remain on therapy. [ABSTRACT FROM AUTHOR]

Background: Endocrine therapy (ET) remains a foundation of systemic therapy for HR+/ HER2- metastatic breast cancer (MBC), although chemotherapy (CT) is used in select patients. In this "real-world" study, we explored treatment patterns, health care resource use (HCRU), costs, adverse events (AEs) and overall survival (OS) in Medicare-enrolled, older patients with HR+/HER2- MBC. Methods: Patients with HR+/HER2- MBC (2007-2011) and aged >66 years were retrospectively analyzed using the SEER-Medicare data. Treatment patterns, HCRU, costs, AEs and OS after MBC diagnosis through end of study period (31 December 2013) were examined using descriptive and multivariable analyses. Results: Among 3622 eligible patients, ET was the most common treatment (77%), followed by CT (50%), radiation (48%) and surgery (19%). The proportion of patients treated with ET monotherapy decreased across therapy lines, from 74% in first line (1 L) to 35% in 4 L. The total number of unique therapy regimens used was 181 in 1 L, 171 in 2 L, 128 in 3 L, and 95 in 4 L. The median OS from MBC diagnosis was 25.3 months (95% CI, 24.0-26.7). In multivariable analyses, receipt of CT and combination CT + ET (versus ET monotherapy) in 1 L, metastatic disease at initial diagnosis, larger tumor size, and presence of visceral and brain metastases at MBC diagnosis significantly predicted receipt of 2 L therapy. Conclusions: ET was the most common first-line treatment for study patients, but its use decreased gradually in the subsequent lines. The heterogeneity in the treatment selection highlights a lack of consensus for the management of HR+/HER2- MBC in routine practice. [ABSTRACT FROM AUTHOR]