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

Identifying patients with hormone receptor-positive (HR+) early invasive breast cancer (EIBC) who benefit from adjuvant chemotherapy has improved with molecular signature tests. However, due to high cost and limited availability, alternative tests are used. The present study 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. From the San José TecSalud Hospital in Monterrey México, patients with HR+ EIBC as tested with EndoPredict or MammaPrint and Ki-67 index were identified. They were categorized into two groups: Group 1 (June 2016-August 2018) was evaluated using EndoPredict and Group 2 (June 2016-August 2018) with MammaPrint. A ≥20% Ki67 index cutoff was utilized to identify highly proliferative EIBC and an area under the receiver-operating characteristic curve and κ concordance were utilized to evaluate the performance of Ki-67 index compared to molecular signature tests. In the EndoPredict group, 54/96 patients were considered high-risk based on their EPclin score, while 57/96 patients had Ki-67 index ≥20%. However, there was no significant overall concordance between them (59.37%, κ=0.168, P=0.09), while the given risk of distant recurrence given in percentage by EPclin had a positive association with the Ki67 index (P=0.04). In the MammaPrint group, 21/70 patients were considered high-risk and 36/70 patients presented with a Ki-67 index ≥20% with a significant overall concordance (67.14%, κ=0.35, P<0.001). In addition, high Ki-67 index was associated with the Nottingham histological grade in both groups. In conclusion, there was a concordance between Ki-67 and MammaPrint risk stratification of HR+ EIBC and no concordance with the EndoPredict molecular signature, but a positive association with the given percentage of recurrence and the median Ki-67 index as the cutoff at our center. Cost-effectiveness analyses of these tests in developing countries are required; until then, the use of Ki-67 appears reasonable to aid clinical decisions, together with the other established clinicopathological variables.