Prognostic significance of Ki67 in Chinese women diagnosed with ER(+)/HER2(−) breast cancers by the 2015 St. Gallen consensus classification

BACKGROUND: This study evaluated the distribution pattern of the Ki67-labeling index (LI) among patients at a Chinese breast cancer center, and analyzed its prognostic significance in the 2015 St Gallen consensus breast cancer classification, estrogen receptor-positive and human epidermal growth factor receptor 2-negative(ER(+)/HER2(−))subtype. METHODS: We classified 939 women with ER(+)/HER2(−) breast cancer into three groups by Ki67-LI levels, and followed their clinicopathologic characteristics and prognoses. RESULTS: In the 939 eligible subjects, 342 had Ki67-LI ≤10% (Ki67(Low)), 281 had Ki67-LI between 10 and 30% (Ki67(Medium)), and 316 had Ki67-LI ≥30% (Ki67(High)). Although the Ki67(High) group had less favorable clinicopathologic factors, the Ki67(Medium) group’s factors varied considerably. Kaplan-Meier estimates showed that disease-free survival(DFS) for the Ki67(Medium) group was significantly shorter than the Ki67(Low) group but longer than the Ki67(High) group. Ki67-LI had independent prognostic significance in multivariate analysis. Other diagnostic factors, including tumor size >2 cm, positive lymph nodes, and grade III disease, were significantly associated with poorer disease-free survival only in the Ki67(Medium) group. CONCLUSIONS: For patients with ER(+)/HER2(−) breast cancer, we confirmed three distinct risk patterns by Ki67-LI levels according to the 2015 St Gallen consensus. For patients with clearly low or high Ki67-LI, straightforward clinical decisions could be offered, but for patients with intermediate Ki67-LI, other factors might provide valuable information. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12885-016-3021-7) contains supplementary material, which is available to authorized users.