Oxytocin Receptor Expression is Associated with Estrogen Receptor Status in Breast Tumors

The oxytocin receptor (OXTR) plays an important role in childbirth, breastfeeding, and social interactions. Increasing evidence exists that OXTR is associated with the breast cancer (BC) initiation and progression. However, the mechanisms leading to its altered expression, the diagnostic or prognostic values of this receptor in BC are currently poorly understood. Here, we have evaluated the relative level of OXTR expression in BC samples (n = 107), and also investigated the effect of estradiol on its expression in MCF-7 and MDA-MB-231 cells. The level of OXTR expression was significantly lower in breast tumor tissue than in normal tissue obtained from the same patient. The OXTR expression depended on the status and expression of the estrogen receptor (ER): the level of OXTR mRNA was significantly lower in ER-negative BC samples compared to ER-positive BC samples. OXTR expression was also lower in samples from patients with luminal subtype with a low value of ER expression (0–5 score according to the IHC assay, Allred scoring) compared with samples with high ER expression (6–8 score). In luminal BC, OXTR expression was associated with the HER2 expression level: the OXTR mRNA level was higher in tumors with the HER2 IHC score of 1+ as compared to cases with the HER2 expression score of 2+, 3+. We also showed that estradiol increased the level of OXTR mRNA in MCF-7 cells, but not in ER-negative MDA-MB-231 cells. The data obtained indicate that changes in OXTR expression in BC tissues can be induced by increased ER expression. We found no association between OXTR and T or N stages and progesterone receptor expression.