Discordance in Oncotype DX Breast Recurrence Score(R) Results for Bilateral Breast Cancer

Background. The Oncotype DX Breast Recurrence Score(R) assay is a clinically useful tool to determine the benefit of chemotherapy in the treatment of early-stage, hormone-receptor-positive breast cancer. Bilateral breast cancer (BBC) is found in similar to 5% of patients with breast cancer, and data regarding discordance of Oncotype DX results between BBC defined by current TAILORx subgroups are limited. Our goals are to study the rate of Oncotype DX discordance between BBC and investigate whether such differences can affect chemotherapy treatment discussions. Methods. Patients with BBC were identified in US samples submitted to Genomic Health for 21-gene testing between January 2019 and July 2020. The risk categories were defined as 0-25 and 26-100 as well as 0-17, 18-30, and 31-100 for all patients. Subgroup analysis was also performed for node-negative women age <= 50 years with Recurrence Score results of 0-15, 16-20, 21-25, and 26-100. Results. 944 BBC patients with known nodal status (702 node negative, 242 node positive) were identified and included. Among node-negative patients aged > 50 years, the rate of discordance in Recurrence Score by group (0-25 and 26-100) was 4.2% (n = 598). For node-negative patients aged <= 50 years, the risk group was discordant in < 3% when considering the risk grouping of 0-25 and 26-100. However, upon subgroup analysis based on TAILORx analysis, the rate of discordance was 48.1% in these younger patients (n = 104). Conclusions. This study shows that a clinically relevant rate of discordance in Oncotype DX results in patients with BBC may impact medical decision-making regarding chemotherapy.