The REMAR (Rhein-Main-Registry) real-world study: prospective evaluation of the 21-gene breast recurrence score® assay in addition to Ki-67 for adjuvant treatment decisions in early-stage breast cancer

Purpose Ki-67 is recommended by international/national guidelines for risk stratification in early breast cancer (EBC), particularly for defining “intermediate risk,” despite inter-laboratory/inter-observer variability and cutoff uncertainty. We investigated Ki-67 (> 10%– < 40%, determined locally) as a prognostic marker for intermediate/high risk in EBC, pN0-1 patients. Methods This prospective, non-interventional, real-world study included females ≥ 18 years, with pN0/pN1mi/pN1, HR+ , HER2-negative EBC, and locally determined Ki-67 ranging 10%–40%. The primary outcome was changes in treatment recommendations after disclosing the Oncotype DX Breast Recurrence Score ® (RS) assay result. Results The analysis included 567 patients (median age, 57 [range, 29–83] years; 70%/1%/29%/ with pN0/pN1mi/pN1 disease; 81% and 19% with RS results 0–25 and 26–100, respectively). The correlations between local and central Ki-67, local Ki-67, and the RS, and central Ki-67 and the RS results were weak ( r = 0.35, r = 0.3, and r = 0.46, respectively), and discrepancies were noted in both directions (e.g., local Ki-67 was lower or higher than central Ki-67). After disclosing the RS, treatment recommendations changed for 190 patients (34%). Changes were observed in pN0 and pN1mi/pN1 patients and in patients with centrally determined Ki-67 ≤ 10% and > 10%. Treatment changes were aligned with RS results (adding chemotherapy for patients with higher RS results, omitting it for lower RS results), and their net result was 8% reduction in adjuvant chemotherapy use (from 32% pre-RS results to 24% post-RS results). Conclusion The Oncotype DX ® assay is a tool for individualizing treatments that adds to classic treatment decision factors. The RS result and Ki-67 are not interchangeable, and Ki-67, as well as nodal status, should not be used as gatekeepers for testing eligibility, to avoid under and overtreatment.