High expression of REGγ is associated with metastasis and poor prognosis of patients with breast cancer.

REGgamma (REGγ) has been recently found in several types of human cancer, however, its clinical significance in metastasis and prognosis of breast cancer remains unknown. In this study, immunohistochemical staining and western blot analysis were performed to evaluate REGγ expression in both mouse and human breast cancer specimens. We found that in MMTV-PyMT mice, 14 out of 20 (70%) mouse mammary carcinomas were REGγ positive, which was significantly higher than control (0/20, 0%, P < 0.001) and lower than metastatic lung tumour (20/20, 100%, P = 0.027). Further investigation for REGγ expression in 136 human breast cancer tissues with the paired peritumoural normal breast tissues and 140 breast benign disease tissue samples showed that REGγ was undetectable in normal breast tissues and nonmetastatic axillary lymph nodes (ALNs), whereas 111 out of 136 (81.6%) breast cancer tissue samples were REGγ positive, which was significantly higher than breast benign disease tissues (9/140, 6.4%, P < 0.001) and lower than metastatic ALNs (116/116, 100%, P < 0.001). The 5-year disease-free and overall survivals of patients with negative/low level of REGγ were significantly higher than those of patients with high level of REGγ (P < 0.05). Cox regression analyses further indicated that REGγ could serve as a novel independent prognostic factor for breast cancer (OR = 4.369, P = 0.008). Our results suggest that the high expression of REGγ might predict metastasis and poor prognosis in breast cancer.