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

Abstract

6584 Background: Studies have shown that a low (<11) Oncotype DX recurrence score (RS) is associated with better survival outcomes. RS is currently included in the AJCC prognostic staging criteria. Not all patients with a low RS are downstaged. It has been suggested that a low RS should further downstage patients regardless of other disease factors. We explored survival outcomes for patients with a low RS to assess if additional patients should be downstaged. Methods: Using the National Cancer Database, female patients ages 18-75 with invasive unilateral pT1-3, pN0-1, M0 hormone receptor positive (ER+ and/or PR+), HER2- breast cancer and a RS <11, diagnosed 2010-2018 were identified. Patients who received neoadjuvant treatment were excluded. Patients were grouped based on the AJCC 8th edition prognostic stage (IA, IB, IIA, IIB, IIIA). Variables were summarized, and unadjusted overall survival (OS) was estimated using the Kaplan-Meier method. Cox proportional hazards models were used to estimate the association of stage with OS after adjustment for available covariates. Results: Of the 54,961 patients with a RS <11, median follow-up was 57.7 months (95% CI 57.3-58.1), and median age was 61yo (IQR 52-67). Most tumors were grade 1 (37.6%) or 2 (56.9%) with ductal histology (75.3%). The median tumor size was 1.5 cm (IQR 1-2), and most were pN0 (83.3%). Although most patients with a RS <11 were stage IA (94.2%), some had a higher stage assignment (5.1% stage IB, 0.6% IIA, 0.1% IIB, <0.01% IIIA). Most patients (93.4%) received endocrine therapy (ET), and few (3%) received chemotherapy. Patients treated with chemotherapy more often had younger age, lobular histology, higher grade, larger tumor size, and/or pN+ disease (all p<0.001). Unadjusted OS was reduced with higher stage (log-rank p<0.001), and this remained true when limited to only those who received ET without chemotherapy (log-rank p<0.001). After adjustment for relevant covariates including treatment, higher stage remained associated with worse OS [stage IA: ref; IB: HR 1.66 (95% CI 1.34-2.05); IIA: HR 2.29 (95% CI 1.44-3.65); IIB: HR 2.48 (95% CI 1.03-5.95); overall p<0.001]. Conclusions: For patients with a low RS, survival outcomes vary with current AJCC prognostic disease stage, suggesting that not all patients with a RS <11 should be downstaged based on RS alone. Anatomic and other non-genomic factors remain relevant when assessing prognosis. [Table: see text]