Background: Immunohistochemical (IHC) expression of Ki67 has a prognostic and predictive value for breast cancer, and the IHC Ki67 labeling index is estimated by counting the number of positive and negative cells. It has not been clarified whether IHC Ki67 estimated using a semiquantitative scoring system has a prognostic value. We aimed to estimate the usefulness of scoring categories of IHC Ki67 as a prognostic factor for breast cancer subgroups.
Patients and methods: We retrospectively identified patients in the Tokai University breast cancer database for whom IHC Ki67 data were available between January 1, 2000 and December 31, 2010. Survival curves were calculated using the Kaplan-Meier method and compared using the log-rank test.
Results: Of the 1331 primary breast cancer patients included in the study, In patients with estrogen receptor (ER)-positive and HER2-negative tumors (n = 971), high and intermediate Ki67 scores were associated with poorer relapse-free survival than low Ki67 scores (P < .001 and P = .002, respectively). Furthermore, in the multivariate analyses of this subgroup, progression-free survival (PFS) was significantly longer in patients with low Ki67 scores than in patients with high Ki67 scores (hazard ratio, 0.387; 95% confidence interval, 0.233-0.643; P < .001). In the multivariate analyses, the Ki67 score was not significantly associated with PFS in the ER-positive and HER2-positive, ER-negative and HER2-positive, or ER-negative and HER2-negative subgroups.
Conclusion: Our data demonstrated that low, intermediate, and high Ki67 scores have a prognostic value in breast cancer patients with ER-positive and HER2-negative tumors.
Keywords: ER; Ki67; Prognostic marker; Proliferation; Subgroups.
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