Expression of enhancer of zeste homolog 2 correlates with survival outcome in patients with metastatic breast cancer: exploratory study using primary and paired metastatic lesions

Abstract

Background: In metastatic breast cancer, the status of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), as well as the Ki-67 index sometimes change between primary and metastatic lesions. However, the change in expression levels of enhancer of zeste homolog 2 (EZH2) between primary and metastatic lesions has not been determined in metastatic breast cancer.

Methods: Ninety-six metastatic breast cancer patients had biopsies or resections of metastatic lesions between September 1990 and February 2014 at the Kanagawa Cancer Center. We evaluated ER, PR, HER2, Ki-67, and EZH2 in primary lesions and their corresponding metastatic lesions using immunohistochemistry. We examined the change in expression of EZH2 between primary and metastatic lesions, the correlation between the expression of EZH2 and the expression of other biomarkers, and the relationship between EZH2 expression and patient outcome in metastatic breast cancer.

Results: EZH2 expression was significantly higher in metastatic lesions compared with primary lesions. EZH2 expression was highly correlated with Ki-67 expression in primary and metastatic lesions. High-level expression of EZH2 was associated with poorer disease-free survival (DFS) outcomes in patients with primary lesions (P < 0.001); however, high-level expression of EZH2 was not associated with poorer DFS outcomes in patients with metastatic lesions (P = 0.063). High-level expression of EZH2 was associated with poorer overall survival (OS) postoperatively in patients with primary (P = 0.001) or metastatic lesions (P = 0.005). High-level expression of EZH2 was associated with poorer OS outcomes after recurrence in patients with metastatic lesions (P = 0.014); however, high-level expression of EZH2 was not associated with poorer OS outcomes after recurrence in patients with primary lesions (P = 0.096). High-level expression of EZH2 in metastatic lesions was independently associated with poorer OS outcomes after recurrence.

Conclusions: EZH2 expression was significantly increased in metastatic lesions compared with primary lesions. High-level expression of EZH2 in metastatic lesions was associated with poorer OS outcomes after primary surgery and recurrence.

Keywords: EZH2; Epigenetics; Immunohistochemistry; Ki-67; Metastatic breast cancer; Prognostic factor.

Fig. 1

Representative breast tissue sections stained with an antibody to EZH2. Representative examples of primary tissue or metastatic tissue cores presenting with five levels of staining for enhancer of zeste homolog 2 (EZH2):a normal breast; b ≤1/100 cells stained (Score 1); c ≤1/10 cells stained (Score 2); d ≤1/3 cells stained (Score 3); e ≤2/3 cells stained (Score 4); and f >2/3 stained (Score 5) (Original magnification, 200× The under bar is 200 μm.)

Fig. 2

Comparison of the Ki67 expression score and EZH2 expression between primary and metastatic lesions. The mean and standard deviation score of (a) Ki67 expression in primary lesions was 2.74 ± 0.92, and in metastatic lesions was 3.10 ± 0.97. The mean and standard deviation score of (b) EZH2 expression in primary lesions was 3.56 ± 1.34, and in metastatic lesions was 4.26 ± 1.08

Fig. 3

Kaplan–Meier survival curves for breast cancer patients (n = 96) with high and low enhancer of zeste homolog 2 (EZH2) expression. Kaplan–Meier survival curves for breast cancer patients with high and low enhancer of zeste homolog 2 (EZH2) expression in (a) disease-free survival in patients with primary lesions, b overall survival in patients after primary surgery with primary lesions, c overall survival in patients after recurrence with primary lesions, d disease-free survival in patients with metastatic lesions, e overall survival in patients after primary surgery with metastatic lesions, and (f) overall survival in patients after recurrence with metastatic lesions