Prognostic impact of Ki-67 overexpression in subgroups categorized according to St. Gallen with early stage breast cancer.

Background: Ki-67 overexpression has been reported to be related to a poor prognosis for early stage breast cancer. We analyzed whether Ki-67 has a prognostic impact on risk subgroups based on the recommendations at St. Gallen in 2007.

Methods: To determine the impact of Ki-67 on each risk group, a retrospective analysis was performed in patients with breast cancer who underwent curative surgery. Ki-67 was examined by immunohistochemistry with a predefined cutoff level of 10%.

Results: A total of 1,166 patients were eligible for this analysis. During the follow-up period, distant metastasis was observed in 164 patients (14.1%), and 80 patients (6.9%) died. Ki-67 overexpression (Ki-67 ≥ 10%) was identified as an independent prognostic factor for distant-metastatic-free survival (DFS) and overall survival (OS) by univariate and multivariate analysis. In the intermediate-risk group, the difference between Ki-67 overexpression and no overexpression was statistically significant in 5-year DFS (90.9 vs. 83.4%, p = 0.002) and OS (98.1 vs. 95.8%, p = 0.002). However, in both the low- and high-risk groups, Ki-67 overexpression was not an independent prognostic factor for either 5-year DFS or OS.

Conclusions: Ki-67 overexpression indicates an unfavorable prognostic impact for DFS and OS. However, this impact is restricted only to those patients classified at intermediate risk.