Human Epidermal Growth Factor Receptor 2-Positive (HER2+) Early Breast Cancer Treatment and Outcomes by Risk of Recurrence: A Retrospective US Electronic Health Records Study

<b>Background/Objectives</b>: This study analyzed real-world data to assess patient characteristics, treatment patterns, and clinical outcomes in patients with human epidermal growth factor receptor 2-positive (HER2+) early breast cancer (eBC), as data for this patient group are limited. <b>Methods</b>: This was a retrospective observational cohort study of patients in a US electronic health record-derived deidentified database. Patient characteristics, treatment patterns, and clinical outcomes were analyzed overall and by risk of recurrence (high-risk versus non-high-risk). <b>Results</b>: Of 1290 patients, 366 (28.4%) were classified as high-risk and 924 (71.6%) as non-high-risk. At 5 years, high-risk versus non-high-risk eBC had a lower probability of invasive disease-free survival (72.3% [95% CI: 66.8-77.1%] vs. 80.7% [95% CI: 77.6-83.5%]), distant recurrence-free survival (78.7% [95% CI: 74.1-83.6%] vs. 89.3% [95% CI: 86.9-91.7%]), and overall survival (86.9% [95% CI: 82.3-90.4%] vs. 91.8% [95% CI: 89.4-93.7%]), and a shorter time to mBC diagnosis (22.6 vs. 34.1 months, respectively). Neoadjuvant therapy use increased from 18.2% in 2011-2013 to 67.3% in 2018-2021 in high-risk eBC and from 4.1% to 34.4% in non-high-risk eBC. However, 32.7% of eligible patients with high-risk eBC did not receive neoadjuvant therapy in 2018-2021. Use of post-neoadjuvant and adjuvant therapy increased in high-risk (but not non-high-risk) eBC from 81.8% in 2011-2013 to 91.8% in 2018-2021. <b>Conclusions</b>: High-risk HER2+ eBC manifested more aggressively than non-high-risk eBC. Utilization of neoadjuvant and (post-neo)adjuvant therapy increased over time. However, despite guideline recommendations, uptake of neoadjuvant therapy remains suboptimal.