Background: The criteria for classifying hormone receptor (HR)-positive/HER2-negative breast cancers into low-risk and high-risk subgroups remain undetermined. Supportive data for optimal criteria to identify tumors in the high-risk subgroup are necessary for Japanese patients with HR-positive/HER2-negative breast cancers.
Methods: Using immunohistochemistry and fluorescence in situ hybridization, we identified 369 consecutive patients with HR-positive/HER2-negative, node-negative invasive breast cancers. We examined the prognostic impact of the Ki-67 labeling index (LI) based on 3 cutoff values, 10, 14, and 20 %, along with that of histological grade (HG) and nuclear grade (NG) by Cox's univariate and multivariate analyses.
Results: The univariate analyses clearly showed that Ki-67 LI with any cutoff value divided the patients into distinct high-risk and low-risk groups, and that HG and NG were also powerful prognostic indicators. High Ki-67 LI with any cutoff value was strongly correlated with HG and NG, and when these parameters were included in the multivariate analyses, the impact of HG/NG was stronger than Ki-67 LIs. When the 10 % cutoff value was adopted, discordance between Ki-67 LI and grades was frequent in papillotubular-type invasive ductal carcinoma, predominantly intraductal carcinoma, and mucinous carcinoma.
Conclusions: Any of the Ki-67 LI values, regardless of cutoff value, could be applicable for the classification of high-risk and low-risk HR-positive/HER2-negative, node-negative invasive breast cancers. Luminal A/B subtyping according to Ki-67 LI, or HG/NG, in combination with histological type, appeared to be able to create an optimum risk estimation system for patients with HR-positive/HER2-negative, node-negative invasive breast cancers in Japan.