Prognostic value of Ki-67 according to age in patients with triple-negative breast cancer

The prognostic value of Ki-67 in triple-negative breast cancer (TNBC) is yet unclear because the cut-off points employed differ widely and its predictive effect may vary according to age. The purpose of this study was to analyze the role of Ki-67 among patients with TNBC, and determine the optimal Ki-67 cut-off point to demonstrate its prognostic relevance associated with patient age and treatment strategy.

201 consecutive patients treated for primary TNBC from 1999 to 2014 were analyzed. Clinicopathological characteristics and outcomes were compared between patients treated with neoadjuvant or adjuvant chemotherapy. We used time-dependent receiver operating characteristic (ROC) curve and time-dependent area under the ROC curve (AUC) to evaluate the discriminative ability of Ki-67 at 3 and 5 years of follow-up. A Ki-67 cut-off point that maximized sensibility and specificity was established. Interaction effect between age and Ki-67 on disease-free survival (DFS) and overall survival (OS) was evaluated by stratified analysis.

According to the coordinates of the ROC curves, the best cut-off point for Ki-67 was 60% (high/low). In the whole group, there was not a statistically significant association between Ki-67 and OS and DFS, using a cut-off point of 60%. In multivariate analysis (COX proportional hazards regression), for DFS high Ki-67 (> 60%) was a poor prognostic factor in patients > 40 years old and a better prognostic factor among the patients < 40 years old.

Prognostic value of Ki-67 in TNBC, using a cut-off point of 60%, may vary depending on age.