Breast cancer staging for patients with "low-risk" disease: Are they all the same?

Contemporary breast cancer staging incorporates anatomic and biologic factors. Although a low (<11) Oncotype Recurrence Score (RS) is linked to favorable survival, it is unclear if RS alone justifies downstaging to pathologic prognostic stage (PPS) IA. This study evaluated whether a low RS equates prognostically to PPS IA.

Patients (18-75 years) with pT1-3/pN0-1/M0, hormone receptor-positive, HER2-negative unilateral invasive breast cancer, diagnosed between 2010 and 2018 were identified from the National Cancer Database. Patients receiving neoadjuvant therapy or lacking RS data were excluded. Patients were grouped by PPS, with overall survival (OS) estimated using Kaplan-Meier and adjusted with Cox models.

Among 231,031 patients, 23.8% had RS < 11, 36.6% had RS 11-17, 25.8% had RS 18-25, and 13.8% had RS > 25. Median follow up was 58.9 months. Most with RS < 11 were PPS IA (94.2%), yet OS declined with higher stage (p < .001). Adjusted analyses showed worse OS for higher stages within RS < 11 (IB: HR 1.66 [95% CI, 1.34-2.05]; IIA: HR 2.29 [1.44-3.65]; IIB: HR 2.48 [1.03-5.95]). In the RS 11-17 group, 90.8% were PPS IA. Five-year OS varied (IA: 97.8%, IB: 95.8%, IIA: 95.2%, IIB: 93.7%, IIIA: 100%; p < .001). Adjusted OS differences persisted (IB: HR 1.51 [1.32-1.73]; IIA: HR 1.32 [1.01-1.72]; IIB: HR 1.58 [0.95-2.63]; IIIA: HR 1.44 (0.21-9.95]).

Prognostic stage significantly influences survival among patients with low RS. RS < 11 alone should not automatically downstage patients to PPS IA; anatomic and other nongenomic factors remain important for prognosis.