Comparison between Ki67 Expression and Oncotype Dx® Recurrence Score in Luminal Breast Carcinomas

Introduction: In early-stage breast cancer, there is a constant search to identify which patients will benefit from chemotherapy. Among the most widely used genetic tests is Oncotype DX®, a validated prognostic marker. However, its high cost is still a major limitation. As a more financially viable alternative, the cell proliferation index determined by the Ki67 antigen is used.Objective: To evaluate the percentage of Ki67 expression and its relationship with the Oncotype DX® recurrence score in luminal breast carcinomas.Methods: 79 Oncotype DX® results available in the last 5 years were analyzed and compared with the respective anatomopathological and immunohistochemical reports.Results: The mean age was 56 years with tumors ≤ 2 cm (72.2%), with a predominance of carcinomas of no special type (73.4%) and tumor grade 2 (72.2%). Among patients under 50 years of age, intermediate risk was the most common (60.7%). In this group, the cutoff point for Ki67 by ROC curve adjustment was 37% (p=0.032), with sensitivity of 85.7% and specificity of 61.9%. In patients over 50 years of age, low risk was prevalent (70.6%). The cutoff point for Ki67 by ROC curve adjustment was 33% (p=0.040), with sensitivity of 93.3% and specificity of 41.7%. For these cutoff points, the kappa coefficient of agreement was estimated at 0.29.Conclusions: Ki67 correlated with the Oncotype DX® recurrence score. The kappa index showed low agreement. The results suggest that Ki67 should not be used alone for therapeutic decision-making, but rather associated with clinical factors.