Background: Ki67 labeling index (Ki67 LI) is a measure of tumor proliferation. In breast cancer, evidence supporting its prognostic value is clear and its predictive value for response to treatment finds some benefits. However, studies of Ki67 LI as a predictive marker in early breast cancer are still limited worldwide and there is no data in Thailand.
Objective: To assess the predictive value of Ki67 expression for adjuvant chemotherapy in patients with node-negative, hormone receptor-positive breast cancer.
Material and Method: The authors retrospectively evaluated 127 diagnosed early breast cancer with node-negative, hormone receptor-positive patients and receiving adjuvant systemic treatment at Siriraj hospital. Disease free survival (DFS) was compared with the log-rank test according to Ki67 LI and adjuvant systemic treatment (chemoendocrine therapy and endocrine therapy alone).
Results: At a median follow-up of 3.3 years. The 5 year DFS rate was 79% for patients with low Ki67 expression and 75% for patients with high Ki67 expression. Of the 127 patients, 56 (44.1%) received chemoendocrine therapy and 71 (55.9%) were treated with endocrine therapy alone. There was no different effect of DFS among those receiving adjuvant endocrine therapy alone and those receiving adjuvant chemoendocrine therapy depending on Ki67 expression.
Conclusion: Among patients with node-negative, hormone receptor-positive breast cancer, a high Ki67 LI had worse DFS trend than a low Ki67 LI but the Ki67 LI did not predict the efficacy of adjuvant chemotherapy.

Keywords: Adjuvant chemotherapy, Ki67, Breast cancer