MZB1 expression indicates poor prognosis in estrogen receptor-positive breast cancer.

Breast cancer (BC) is the most common malignant tumor in females. Development of novel biomarkers or therapeutic targets may contribute toward the improvement of a patient's prognosis. Marginal zone B and B1 cell-specific protein (MZB1) is an unfolded protein response-related chaperone and mainly exists in the endoplasmic reticulum of B lymphocytes, although little is known regarding its role in BC cells. The present study aimed to investigate the significance of MZB1 expression in BC. To begin with, mRNA expression levels in 13 BC cell lines and two non-cancerous mammary cell lines were evaluated. Next, mRNA and protein expression of MZB1 in BC patient tumor specimens was evaluated to assess the association between expression and clinicopathological factors or prognosis. mRNA expression levels were detectable in four estrogen receptor (ER)-positive BC cell lines. When ratios of mRNA expression levels between BC and non-cancerous specimens were evaluated, patients with stage III disease exhibited a higher ratio than patients with stage 0/I/II disease (P=0.009). Using immunohistochemistry, patients with ER-positive BC more frequently expressed MZB1, compared with patients with ER-negative BC (P=0.003). In patients with ER-positive BC, patients with MZB1-positive BC experienced shorter disease-free survival (DFS) times than patients with negative BC (P=0.026). Multivariate analysis of DFS demonstrated that MZB1 positivity was an independent prognostic factor (P=0.022). The results of the present study suggested that MZB1 expression may be associated with a more advanced stage of BC. Furthermore, in patients with ER-positive BC, MZB1 may be a potential prognostic marker.