The oxytocin receptor (OXTR) plays an important role in childbirth, breastfeeding, and social interactions. There is emerging evidence that OXTR is associated with the breast cancer (BC) initiation and progression. However, the mechanisms leading to a change in its expression, the diagnostic or prognostic value of the 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 expression of OXTR was dependent 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. Moreover, 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 a 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. These data indicate that changes in OXTR expression in BC tissues can be caused by increased ER expression. We found no association between OXTR and T or N stages and progesterone receptor expression.Retseptor oksitotsina (OXTR) igraet vazhnuiu rol' v protsessakh detorozhdeniia, grudnogo vskarmlivaniia i sotsial'nykh vzaimodeĭstviĭ. V poslednie gody poiavilis' dannye v pol'zu togo, chto OXTR sviazan s razvitiem i progressirovaniem raka molochnoĭ zhelezy (RMZh). Odnako mekhanizmy, privodiashchie k izmeneniiu ego ékspressii, diagnosticheskaia ili prognosticheskaia tsennost' retseptora pri RMZh na dannyĭ moment maloizuchenny. Poétomu my postavili tsel' otsenit' uroven' ékspressii OXTR v obraztsakh RMZh (n=107), a takzhe issledovat' vliianie éstradiola na ego ékspressiiu v kletkakh liniĭ MCF-7 i MDA-MB-231. Uroven' ékspressii OXTR byl znachitel'no nizhe v opukholevoĭ tkani molochnoĭ zhelezy, chem v normal'noĭ tkani, vziatoĭ ot togo zhe patsienta. Ékspressiia OXTR zavisela ot statusa i ékspressii éstrogenovogo retseptora (ER): uroven' mRNK OXTR byl dostoverno nizhe v obraztsakh ER-negativnogo RMZh po sravneniiu s obraztsami ER-pozitivnogo RMZh. Ékspressiia OXTR byla nizhe v obraztsakh patsientov s liuminal'nym RMZh pri nizkom znachenii ékspressii ER (0-5 ballov soglasno immunogistokhimicheskomu (IGKh) issledovaniiu, shkala Allred) po sravneniiu s obraztsami s vysokoĭ ékspressieĭ ER. Uroven' mRNK OXTR byl assotsiirovan s urovnem ékspressii HER2: uroven' mRNK OXTR byl znachitel'no povyshen v obraztsakh liuminal'nogo RMZh s urovnem ékspressii HER2 1 ball, soglasno IGKh issledovaniiu, po sravneniiu s opukholiami s vysokoĭ ékspressieĭ HER2 (2-3 balla). My takzhe pokazali, chto pod deĭstviem éstradiola uvelichivalsia uroven' mRNK OXTR v kletkakh MCF-7, no ne v ER-negativnykh kletkakh MDA-MB-231. Poluchennye dannye ukazyvaiut na to, chto izmenenie ékspressii OXTR v tkaniakh RMZh mozhet byt' vyzvano usileniem ékspressii ER. Sviazi OXTR so statusom T ili N opukholi i ékspressieĭ progesteronovogo retseptora vyiavleno ne bylo.