Background: A systematic literature review was conducted to summarize first-line (1L) treatments and clinical outcomes among patients with hormone receptor-positive (HR+), human epidermal growth factor 2-positive (HER2+) advanced or metastatic breast cancer (aBC).Methods: Clinical trials and real-world studies (RWS) published between 01/2000-12/ 2020 evaluating clinical outcomes of 1L treatments in adults with HR+/HER2+ aBC were identified through pre-specified searches in Medline, Embase, Cochrane Library, and key conference proceedings. Study and patient characteristics, treatments (anti-HER2 therapy [AHT]+chemotherapy [CT], AHT+endocrine therapy [ET], ET only, and AHT only), treatment strategy (no induction vs. induction and maintenance), and outcomes (e.g., progression-free survival [PFS], overall survival [OS]) were extracted and summarized.Results: Overall, 20 trials and 21 RWS were identified. Among trials, treatments with AHT+CT (70%), AHT+ET (17%), ET only (10%), and AHT only (3%) were evaluated across 30 study arms. Fourteen of these study arms included induction and maintenance treatments, of which induction with AHT+CT (79%), CT only (14%), and AHT only (7%) were evaluated. Median PFS and OS ranged from 2.4-23.7 months and 23.9-66.7 months, respectively, in trials. Among RWS, AHT-based regimens (71%), ET alone (10%), CT alone (5%), or a combination (15%) were evaluated across 41 study arms. Eleven (27%) and 3 (7%) study arms assessed treatments in the induction and maintenance setting and with no induction therapy, respectively, while 27 (66%) could not be evaluated. Induction regimens used included AHT+CT (82%), AHT only (9%), and ET only (9%). Real-world median PFS and OS ranged from 4.8-29.0 months and 26.0-80.4 months, respectively. All studies measured PFS/OS from any 1L treatment initiation for aBC or earlier.Conclusions: There is considerable variation in treatments and clinical outcomes in this patient population. Though most real-world patients with HR+/HER2+ aBC receive AHT-based regimens in the 1L setting, few also receive ET.
