Predictive impact of retinoid X receptor-alpha-expression in renal-cell carcinoma

Retinoid receptors are nuclear transcription factors that mediate the effects of retinoids on gene expression. In our study, we analyzed the expression of retinoid X receptor-alpha (RXR-alpha) and its prognostic value in renal-cell carcinoma (RCC) patients exhibiting stage IV disease upon first diagnosis or thereafter.

Detection of RXR-alpha was performed on tumor specimens from 63 patients with primary RCC, using immunohistochemical techniques. For our evaluation of the immunostaining results, we developed a new cell-counting system based on the subcellular distribution of immunoreactivity. The impact of the subcellular distribution of RXR-alpha on the prognosis of patients with RCC was analyzed statistically among other clinicopathologic factors. The primary end point was survival.

In 34 RCC samples (54.0%), RXR-alpha was detected predominantly in the nucleus, while 25 RCC specimens (39.7%) displayed an aberrant subcellular distribution pattern, with a predominantly cytoplasmic staining with nuclear sparing in 15 specimens (23.8%), and a combined nuclear and cytoplasmic staining in 10 specimens (15.9%). Very faint to undetectable immunoreactivity was noted in 4 cases (6.3%) of RCC. Univariate Kaplan-Meier analysis showed that patients with a predominantly nuclear localization of RXR-alpha had a significantly prolonged survival after primary tumor diagnosis, when compared to patients with a predominantly aberrant subcellular distribution profile (p < 0.01). Furthermore, multivariate analysis revealed that an aberrant subcellular distribution of RXR-alpha in RCC was an independent predictor of poor survival (p < 0.01).

Our study indicated that the subcellular intratumoral distribution pattern of RXR-alpha could independently predict the survival of RCC patients. However, the exact mechanisms underlying the aberrant compartmentalization and the functions of RXR-alpha in RCC remain to be determined.