Comparison of diversity across real-world evidence, randomized clinical trial, and Surveillance, Epidemiology, and End Results (SEER) data in patients with metastatic breast cancer

e18670 Background: Compared with patients in typical care settings, participants in randomized clinical trials (RCTs) tend to be younger and less diverse. We compared representation of age, race, and ethnicity at initiation of first-line (1L) therapy for metastatic breast cancer across real-world evidence (RWE), RCT, and Surveillance, Epidemiology, and End Results (SEER) registry data. Methods: RWE and SEER inclusion criteria were based on corresponding RCTs. We compared age, race, and ethnicity at initiation of 1L therapy among female patients with metastatic breast cancer across 2 RWE chart review studies (completed between 2019-2021), 4 RCTs with similar eligibility (reported between 2014–2021), and the latest SEER registry data (2017–2019) using t-tests and 2-sided chi-square tests. Results: We collected demographics of 57,479 patients (RWE: n = 860, 1.5%; RCT: n = 2,707, 4.7%; SEER: n = 53,912, 93.8%). Mean age at 1L therapy initiation was significantly higher in RWE than RCT studies (61.8 vs 56.0 years) and representation of Black patients was significantly higher in RWE than RCT studies (25.3% vs 2.9%), both P< .001. Mean age at metastatic diagnosis in SEER was 59.0 years; age at 1L initiation was not reported. SEER included 13.4% Non-Hispanic Black patients. Hispanic representation was 11.2% in RWE, not reported in RCT, and 15.9% in SEER studies (Table). Conclusions: Decisions about treatment choices among clinicians and payers are primarily driven by RCT results, yet they may not be representative of real-world populations. We found that RCTs had lower representation of older and Black patients than both SEER and RWE studies. Limitations included varying study periods, lack of Hispanic ethnicity reporting in RCTs, differential SEER participation by US region, and potential patient overlap. Well-conducted RWE studies may fill gaps left by RCTs for improving representation and generalizability to patients with metastatic breast cancer. [Table: see text]