21-Gene Recurrence Score Testing in HER2-positive Patients

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.