Brother of the Regulator of Imprinted Sites (BORIS) has a role in intracellular signalization and is important in epigenetic mechanism control, such as methylation/demethylation of DNA and histones. BORIS may deregulate some tumor suppressor genes. Immunohistochemical expression of BORIS was found in different tumors, some of them showing correlation with poor prognosis. The aim of this study was to determine immunohistochemical expression of BORIS in pure seminomas and different components of testicular mixed germ cell tumors (MGCT). In this study, immunohistochemical expression of BORIS in testicular germ cell tumors (TGCT) was analyzed. Staining intensity and percentage of positive staining cells were used to evaluate the level of expression. Tumor samples from 44 patients were analyzed; 26 pure seminomas and 18 MGCT. In MGCTs, seminoma component was found in 4, yolk sac in 7, teratoma in 11 and embryonal carcinoma in 13 samples. Expression of BORIS was strong in 80.8% of seminoma cases and in 76.9% of embryonal carcinoma component, 71.4% of yolk sac, 63.6% of teratoma component and 25% of seminomatous component of MGCT. In MGCT, positive correlation was found between BORIS expression in teratomatous component and presence of yolk sac component (BORIS (engl. Brother of the Regulator of Imprinted Sites) sudjeluje u unutarstaničnoj signalizaciji i kontrolira epigenetske mehanizme kao što su metilacija/demetilacija DNK i histona. Aktivacija BORIS-a dovodi do poremećaja određenih tumorskih supresora. Imunohistokemijska izraženost BORIS-a utvrđena je u različitim tumorima. U nekim tumorima nađena je korelacija s lošijom prognozom. Cilj ovoga istraživanja bio je utvrditi imunohistokemijsku izraženost BORIS-a u čistim seminomima i različitim komponentama miješanih tumora zametnih stanica testisa (engl. mixed germ cell tumors, MGCT). Materijal i metode: Analizirana je imunohistokemijska izraženost BORIS-a u tumorima zametnih stanica testisa (engl. testicular germ cell tumors, TGCT), a intenzitet bojenja i postotak reaktivnih stanica korišten je za evaluaciju razine ekspresije. Analizirani su uzorci tumora 44 bolesnika; 26 čistih seminoma i 18 MGCT. Kod MGCT-a komponenta seminoma nađena je u 4, yolk sac-a u 7, teratoma u 11 te embrionalnog karcinoma u 13 uzoraka tumora. Rezultati: Imunohistokemijska izraženost bila je jaka kod 80,8% čistih seminoma te kod 76,9% komponente embrionalnog karcinoma, 71,4% yolk sac-a, 63,6% teratoma i 25% seminomske komponente MGCT-a. Dobivena je pozitivna korelacija izraženosti BORIS-a teratomske komponente i prisutnosti komponente yolc sac
