['We examined hypoxia-inducible protein 2, hypoxia-inducible factor-1alpha and nuclear factor-kappaB in acquired cystic disease of the kidney associated with renal cell carcinoma to elucidate the roles of these factors in cyst formation and subsequent tumor transformation.', 'Immunohistochemical expression of hypoxia-inducible protein 2, hypoxia-inducible factor-1alpha and phosphorylated nuclear factor-kappaB (active form) were examined in 20 normal kidney samples obtained from nephrectomy for localized renal cell carcinoma and 25 kidneys with acquired cystic disease associated renal cell carcinoma from 23 patients on dialysis.', 'Only faint or weak immunostaining for hypoxia-inducible protein 2, hypoxia-inducible factor-1alpha and phosphorylated nuclear factor-kappaB was observed in normal kidney tissues. In nontumor areas of the kidneys with acquired cystic disease expressions of these 3 proteins was up-regulated in tubular and cyst epithelial cells. Acquired cysts were classified into 3 types according to cyst epithelium morphology, namely flat, cuboidal and hyperplastic. Hyperplastic cysts were the predominant cysts expressing hypoxia-inducible protein 2 and hypoxia-inducible factor-1alpha. Although up-regulation of hypoxia-inducible protein 2, hypoxia-inducible factor-1alpha and phosphorylated nuclear factor-kappaB was observed in renal cell carcinoma, positive hypoxia-inducible protein 2 immunostaining was detected predominantly in papillary renal cell carcinoma, while positive hypoxia-inducible factor-1alpha and phosphorylated nuclear factor-kappaB immunostaining was prominent in clear cell renal cell carcinoma.'] Is over expression of hypoxia-inducible protein 2 , hypoxia-inducible factor-1alpha and nuclear factor kappaB putatively involved in acquired renal cyst formation and subsequent tumor transformation in patients with end stage renal failure?