Ciljevi: Osteopontin (OPN) je fosforilirani glikoprotein koji posjeduje različita djelovanja uključujući nastanak i metastaziranje tumora. Kočenje apoptoze jedan je od mehanizama kojim OPN doprinosi napredovanju tumora, a jezgreni čimbenik kappa B (NF-κB) je uključen u signalne putove kočenja apoptoze. Cilj ovog istraživanja je proučavanje izražaja OPN-a u normalnom tkivu bubrega i svijetlostaničnom karcinomu bubrežnih stanica (SKBS) i određivanje njegovog prognostičkog značenja te ujedno određivanje odnosa između NF-κB i izražaja OPN-a na proteinskoj i genskoj razini kao i njihovog odnosa prema apoptozi u uzorcima SKBS-a. Materijali i postupci: Izražaj proteina OPN-a istražen je metodom imunohistokemije na standardnim tkivnim rezovima 171 SKBS-a i uspoređen s uobičajenim kliničkopatološkim čimbenicima. Korištenjem imunohistokemijske metode i tehnike tkivnih mikroareja (TMA) na 94 SKBS-a određen je izražaj proteina OPN-a te p50 i p65 podjedinice NF-κB i međusobno uspoređen kao i s apoptotičkom aktivnosti. Korištenjem kvantitativne lančane reakcije polimerazom (QPCR) određena je količina OPN glasničke RNA (mRNA) iz svježe smrznutog tumorskog tkiva i uspoređena s izražajem proteina OPN-a i NF-κB u 22 SKBS-a. Rezultati: Izražaj OPN-a je u tumorskom tkivu bio veći u odnosu na normalno tkivo bubrega i primijećen je u 61 SKBS-u (35.7 %) kao citoplazmatsko bojanje različite jačine. Utvrđena je povezanost povećanog izražaja OPN-a s pokazateljima loše prognoze kao što su veličina tumora (p<0.001), Fuhrmanov nuklearni gradus (p<0.001), patološki stadij (p=0.011) i Ki-67 indeks proliferacije (p<0.001) te kraće preživljavanje bolesnika (p=0.004). Citoplazmatsko NF-κB bojanje primijećeno je u tumorskim stanicama kao i dobroćudnim strukturama dok je nuklearno bojanje primijećeno većinom u tumorskim stanicama. Utvrđena je korelacija pojačanog izražaja OPN-a na proteinskoj (p<0.001) i genskoj razini (p=0.019) s aktivacijom NF-κB i smanjenjem indeksa apoptoze u tumorskim stanicama (p=0.009). Aktivacija obje NF-κB podjedinice također je obrnuto korelirala s indeksom apoptoze (p=0.003). Zaključak: Pojačan izražaj OPN-a doprinosi napredovanju SKBS-a vjerojatno posredujući kočenje apoptoze putem aktivacije NF-κB. Objectives: Osteopontin (OPN) is a phosphorylated glycoprotein with diverse functions including tumorigenesis and tumor cell metastasis. Apoptosis inhibition is one of the OPN’s mechanisms that contribute cancer progression and nuclear factor-kappa B (NF-κB) is involved in antiapoptotic signaling pathway. The aim of this study was to analyze the expression of OPN in normal renal tissue and clear cell renal cell carcinomas (CRCC), and to assess its prognostic significance together with determining relations between NF-κB and OPN expression at protein and gene level as well as their relation to apoptosis in specimens of CCRCC. Material and Methods: The expression of OPN protein was analyzed using immunohistochemistry in whole-tissue sections of 171 CRCC and compared to usual clinicopathological parameters. Using tissue microarray (TMA) and immunohistochemical technique the expression of OPN protein and p50 and p65 NF-κB subunits was analyzed in 94 CCRCC and compared mutually and to apoptotic index. Using real-time PCR OPN mRNA was quantified from snap frozen tumor tissue and compared to OPN and NF-κB protein expression in 22 CCRCC. Results: Compared to normal renal parenchyma OPN was upregulated in tumor tissue and was observed in 61 CRCC (35.7%) in the form of cytoplasmic staining of various intensities. The association of OPN expression and poor prognostic indicators as tumor size (p<0.001), Fuhrman nuclear grade (p<0.001), pathological stage (p=0.011) and Ki-67 proliferation index (p<0.001) as well as shorter patients survival (p=0.004) was found. Cytoplasmic NF-κB staining was observed in tumor cells and benign elements, while nuclear staining was detected mainly in tumor cells. The correlation of high OPN expression at protein (p<0.001) and gene level (p=0.019) with NF-κB activation as well as decrease of apoptotic index in tumor cells (p=0.009) was found. Activation of both NF-κB subunits also correlated with decreased apoptotic index (p=0.003). Conclusion: Overexpression of OPN contributes the progression of CRCC probably by inhibition of apoptosis through NF-κB activation.