Clinical significance of the 21-gene signature (Oncotype DX) in hormone receptor-positive early stage primary breast cancer in the Japanese population.

BACKGROUND: The 21-gene signature has been intensively studied and incorporated into major guidelines for treatment decision in early breast cancer. However, it remains to be examined whether this system is applicable to Asian populations.
METHODS: The authors collected 325 tumor tissues from estrogen receptor (ER)-positive primary breast cancer patients who had undergone surgery and were treated with tamoxifen between 1992 and 1998. The tissues were analyzed for the 21-gene signature, and the patients were classified into groups of low, intermediate, or high risk based on the Recurrence Score.
RESULTS: A total of 280 patients were eligible, with adequate reverse transcription polymerase chain reaction profiles for the Recurrence Score. Of those, 200 and 80 patients had lymph node-negative and lymph node-positive disease, respectively. The proportions of lymph node-negative patients categorized as being at low, intermediate, or high risk were 48%, 20%, and 33%, respectively. In lymph node-negative patients, the Kaplan-Meier estimates of the distant recurrence rate at 10 years were 3.3% (95% confidence interval [95% CI], 1.1-10.0%), 0%, and 24.8% (95% CI, 15.7-37.8%) for those in the low-risk, intermediate-risk, and high-risk groups, respectively. The risk of distant recurrence in the low-risk group was significantly lower than that in the high-risk group when the entire Kaplan-Meier plots were compared (P < .001, log-rank test). There was a significant difference for overall survival between the low-risk and the high-risk groups (P = .008, log-rank test).
CONCLUSIONS: This is the first report to show that the 21-gene signature has value in providing prognostic information in Asian populations with ER-positive, lymph node-negative breast cancer.