Objective  To investigate the expression and clinical significance of retinoic acid receptor-related orphan receptor-γ (ROR-γ) in triple-negative breast cancer (TNBC).

  Methods  Differences in mRNA expression of ROR-γ between invasive breast cancer and adjacent tissues were analyzed via databases on the Oncomine website. The prognostic significance of ROR-γ in different molecular subtypes of breast cancer was evaluated using the Kaplan-Meier Plotter website. The tissue specimens and clinicopathological data of 269 TNBC patients admitted to Tianjin Medical University Cancer Institute and Hospital from January 2011 to December 2014 were collected. Immunohistochemistry (IHC) was performed to investigate the expression of ROR-γ protein in TNBC patients and validate the relationship between ROR-γ expression and the clinical-pathological features and prognosis of the patients.

  Results  Data analysis results on the Oncomine and Kaplan-Meier Plotter websites showed that the expression of ROR-γ mRNA in invasive breast carcinoma tissues was significantly higher than that in adjacent tissues (P<0.0001). Compared with other molecular subtypes, ROR-γ shows a more significant prognostic value in TNBC, related to poor prognoses. IHC results showed that the expression of ROR-γ protein in TNBC tissue was higher than that in adjacent tissues; the high expression rate of ROR-γ in TNBC tissue was 18.2% (49/269). Patients with high ROR-γ expression tended to have an older onset age (P=0.001), a postmenopausal state (P<0.001), a high tumor Ki-67 index (P=0.001), and lymph node metastasis (P=0.003). High ROR-γ expression is an independent influencing factor for the disease-free survival (P=0.031) and overall survival (P=0.029) of TNBC patients.

  Conclusions  ROR-γ is highly expressed in TNBC tissues and is associated with high tumor proliferation, lymph node metastasis, and poor prognosis. Furthermore, ROR-γ may serve as a potential prognostic marker, providing a new reference for the diagnosis and treatment of TNBC.