Correlation between Ki-67 proliferation index in invasive breast cancer and molecular signatures: EndoPredict and MammaPrint

Background: The need to identify patients with hormone receptor-positive (HR+) early invasive breast cancer (EIBC) who could benefit from adjuvant chemotherapy has been enhanced with the development of molecular signature tests. However, due to their high cost and limited availability alternative low-cost prognostic and predictive tests are used in clinical practice. Here, we sought to evaluate the performance of the proliferation marker Ki-67 to identify these patients and explore its association with molecular signatures and risk stratification markers. Methods: From our prospectively maintained multicenter breast cancer registry, we identified EIBC HR+ patients tested with EndoPredict or MammaPrint and Ki-67 as part of their routine workup. Patients were categorized into two groups: Group 1 (2016-2018) was evaluated using EndoPredict and Group 2 (2011 to 2018) with MammaPrint. A ≥20% Ki67 cutoff was utilized for identify high proliferative EIBC and a receiver-operative curve area under the curve (AUC) and kappa concordance were utilized to evaluate the performance of Ki-67 compared to molecular signature tests. Results: In the EndoPredict group, 54/96 patients were considered high-risk by EPclin. 57/96 patients had a Ki-67 ≥20%. However, there was no significant overall concordance between them (59.37%, κ = 0.168, p =0.09). In the MammaPrint group, 21/70 patients were considered high-risk. Ki67 ≥20% was present in 36 patients with a significant overall concordance (67.14%, κ 0.35, p<0.001). Additionally, Ki-67 was associated with the Nottingham histological grade (NHG) in both groups. Conclusion: There is a fair concordance between Ki-67 and MammaPrint risk stratification of HR + EIBC and no concordance with EndoPredict molecular signature. Cost-effectiveness analysis of these tests in developing countries are needed, until then, the use of Ki-67 seems reasonable to aid clinical decision.