LAUSR

Introduction: The 21‐gene recurrence score (RS) has been extensively studied and validated in patients with estrogen receptor‐positive (ER+), human epidermal growth factor 2 (HER2)‐negative breast cancer; however, RS testing is not routinely performed in patients with HER2‐positive (HER2+) disease. We sought to determine patterns of RS testing, to characterize RS distributions, and to determine the impact of RS results on clinical decision‐making for patients with ER+, HER2+ breast cancer. Materials and Methods: Using the Surveillance and Epidemiology End Results program database, we identified women with ER+, HER2+ breast cancer. We stratified patients using TAILORx RS cutoffs and evaluated treatment characteristics across patients. Multivariable logistic regression was performed to determine factors associated with RS testing and receipt of a high‐risk RS. Results: Overall, 5% of patients with ER+, HER2+, early stage breast cancer underwent RS testing. The distribution of RS testing by TAILORx cutoffs were: high‐risk, 17%; intermediate‐risk, 49%; and low‐risk, 34%. Chemotherapy utilization among those not tested was 66%. Among those tested, utilization was significantly associated with RS results: 67% of high‐risk, 30% of intermediate‐risk, and 19% of low‐risk patients received chemotherapy. Progesterone receptor‐negative status, larger tumor size, and high tumor grade were significantly associated with high‐risk RS. Conclusions: RS testing is used sparingly among patients with HER2+ early‐stage breast cancer; however, test results appear to impact clinician's decision‐making on chemotherapy use.