Oncotype DX testing in node-positive breast cancer strongly impacts chemotherapy use at a comprehensive cancer center

In 2016, we initiated standardized "reflex" Oncotype DX Recurrence Score (RS) testing for patients ≤ 65 years with pT1-2N0-1 HR⁺/HER2^- breast cancer. Here, we examine RS testing patterns, RS distribution, and factors associated with chemotherapy use in patients with pN1 breast cancer.

Patients with stage I-III HR⁺/HER2^- pN1 breast cancer treated with upfront surgery from February 2016 to March 2019 were identified. Clinical characteristics were compared between patients meeting reflex RS testing criteria, those with RS ordered outside of reflex criteria, and those without RS testing. RS was categorized as low (< 18), intermediate (18-30), and high (≥ 31). Multivariate logistic regression was performed to identify factors associated with adjuvant chemotherapy receipt. We examined 3-year recurrence-free survival (RFS) and overall survival (OS) stratified by chemotherapy use.

We identified 347 HR⁺/HER2^- pN1 patients; 272 (78.4%) received RS testing, and 194 (71.3%) met reflex criteria. RS was < 18 in 164 (61.4%) patients, 18-30 in 89 (32.7%) patients, and ≥ 31 in 16 (5.9%) patients. On multivariate analysis, RS < 18 (OR 0.47, 95% CI 0.24-0.92) was associated with lower odds of chemotherapy use, whereas presence of lymphovascular invasion (OR 1.77, 95% CI 1.03-3.07) and lobular subtype (OR 2.40, 95% CI 1.21-4.78) were associated with higher odds. No differences in 3-year RFS (p = 0.97) or OS (p = 0.19) based on chemotherapy receipt were observed.

Most RS-tested HR⁺/HER2^- pN1 patients at our center had low genomic risk. A low RS independently influenced chemotherapy omission and in RS-tested patients, short-term outcomes were excellent. Our study demonstrates increased use of RS in guiding adjuvant treatment decisions in node-positive disease.