G-protein-coupled receptor 30 (GPR30) has been reported to be a novel estrogen receptor a (ERa) in vitro. Therefore, the interactions among GPR30, ERa, progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER-2/neu), and their prognostic utilities in the infiltrating ductal carcinoma (IDC) of the breast were evaluated.

Messenger RNA (mRNA) levels of GPR30, ERa, PR and HER-2/neu in the tumor samples of 118 Taiwanese IDC patients and 27 non-tumor mammary tissues were measured via quantitative polymerase chain reaction analyses. The correlations of GPR30 mRNA levels with clinical parameters, i.e. tumor/non-tumor, ERa, PR, HER-2/neu, age, lymph node metastasis, lymph–vascular invasion, grade, stage and patient survival, were assessed by using appropriate statistical analyses.

GPR30 expression was observed to be lower in IDC (p < 0.001) than in non-tumor mammary tissues. Importantly, GPR30 mRNA level was positively correlated with that of ERa (p = 0.001) and PR (p = 0.001) but not correlated with that of HER-2/neu when they were analyzed as continuous variables. However, lower GPR30 was noticed in tumors with HER-2/neu protein overexpression. GPR30 expression was not correlated with age, lymph node metastasis, lymph–vascular invasion, grade and stage in IDC. GPR30 expression was not an independent prognostic factor for patient survival.

GPR30 expression is downregulated in IDC. GPR30 is preferentially co-expressed with ER and/or PR but is lowly expressed in HER-2/neu(+) tumors. The correlation of GPR30 expression with clinical parameters, including patient survival, was not evident in this cohort.