Expression of hypoxia-inducible protein 2 in renal cell carcinoma: A promising candidate for molecular targeting therapy.

This study investigated the expression of hypoxia-inducible protein 2 (HIG2), a novel renal cell carcinoma (RCC)-associated molecule and an essential growth factor for RCC, in kidneys to elucidate its clinical significance in RCC. An immunohistochemical study of HIG2 was conducted in 93 surgical samples of RCC tissues and 10 samples of normal kidney tissues obtained after nephrectomies for localized RCC. HIG2 expression was also correlated with clinicopathological characteristics and survival. Only faint or weak immunostaining for HIG2 was observed in normal kidney samples. HIG2 expression was found in 86% of RCC tissues (80/93). When analyzed by histological type, positive staining for HIG2 was detected in all papillary (7/7), chromophobe (1/1) and cyst-associated (3/3) RCC. In contrast, the HIG2 expression was observed in 85% of clear cell (68/80) and 50% of spindle cell (1/2) RCC. Labeling indices were 74.1, 45.4, 39, 24.8 and 12.1% in papillary, spindle, clear cell, cyst-associated and chromophobe RCC, respectively. A significant increase in HIG2 expression was noted in RCC tissues obtained from patients with high stage RCC, lymph node metastasis and high nuclear grade (p<0.001, p<0.02 and p<0.006, respectively). RCC patients with a negative HIG2 staining had prolonged 5-year cancer-specific survival. In conclusion, HIG2 expression was extensively observed in RCC tissues and was higher in advanced RCC, suggesting that HIG2 is a candidate for the development of molecular targeting therapy.