Alteration of bone sialoprotein expression in osseous metastasized renal cell carcinomas and the tumor surrounding tissue

Bone sialoprotein (BSP) regulates bone metabolism by directly influencing the activity of osteoblasts and osteoclasts. A significant correlation between the tissue expression of BSP in tumors and the occurrence of bone metastases was found in different cancers. Aim of this study was to identify the BSP expression in renal cell carcinomas (RCC) according to their stage of metastatic disease. Tissue samples of patients with RCC who underwent partial resection or nephrectomy were separated into three groups, each with 10 patients showing either no metastases (group I), only soft tissue metastases (group II) or bone metastases (group III) at date of surgery. Immunohistochemical analysis of BSP expression in tumor tissue and corresponding renal parenchyma was performed and evaluated with an established semiquantitative scoring system. BSP expression was detected both in tumor tissue and renal parenchyma. Concerning the expression in malignant tissue, no significant difference could be found between the three groups whereas the corresponding renal parenchyma showed a staining score of 164, 198 and 224 for group I, II and III (P = 0.07). RCC staged T3 showed only a little higher BSP expression than those staged T1/2 (P < 0.21), while the corresponding parenchyma of T3 tumors showed significantly higher expressions (P = 0.02). This pilot study revealed a correlation between expression of BSP and tumor staging and type of metastases, especially for osseous metastases in RCC. Alternation of BSP expression could be detected particularly in renal parenchyma and linked to the type of metastases.