Histological grade as an alternative to the Ki67 labeling index is only available for luminal-type breast cancers

The 2011 St. Gallen Consensus Statement advocated using histological grade (HG) as a proliferation marker of breast cancer (BC) if reliable Ki67 labeling index (Ki67-LI) assessment is not available. However, it has been difficult to evaluate tumor aggressiveness in case of HG2.

A total of 259 cases of BC were assessed for HG, Ki67-LI and other clinicopathological features. The cut point for Ki67-LI was interpreted as low and high using a 14 % threshold.

The average age at diagnosis was 58.2 years (range 28–86); 64.9 % of the patients were postmenopausal. Of the 259 cases, 151 were stage I, 78 were stage II, 29 were stage III, and 1 was stage IV. The subtypes based on immunohistochemical staining were 60 cases of luminal A (LA) type (23.2 %), 37 cases of luminal B (LB) (HER2−) type (14.3 %), 91 cases of LB (HER2+) type (35.1 %), 40 cases of human epidermal growth factor receptor 2 (HER2) type (15.4 %) and 31 cases of triple negative (TN) type (12 %). HG was 1 (89 cases, 34.4 %), 2 (117 cases, 45.2 %) and 3 (53 cases, 20.5 %). High Ki67-LI cases were observed in HG1 (37.1 %), HG2 (56.4 %) and HG3 (96.2 %). Especially in cases of HG2, high Ki67-LI cases were observed in 0 % of LA type, 100 % of LB (HER2−) type, 71.2 % of LB (HER2+) type, 68.8 % of HER2 type and 40.0 % of TN type. The average Ki67-LI was 6.0 ± 3.8 (LA type), 31.4 ± 15.7 [LB (HER2−) type], 20.2 ± 14.8 [LB (HER2+) type], 32.7 ± 21.9 (HER2 type) and 55.7 ± 32.2 (TN type). All LA-type cases and 66.7 % of LB (HER2+)-type cases were low Ki67-LI.

Our study demonstrates that all LA-type cases and most HG1 of LB (HER2+)-type cases are low proliferative. However, HG was not informative enough for estimating tumor proliferation in cases of LB (HER2−), HER2 and TN types. It is necessary to add other proliferation tools such as the gene expression profiling tool and Ki67-LI except in LA and HG1 of LB (HER2+)-type cases.