Expression of osteopontin and CD44 molecule in papillary renal cell tumors

The aim of the study was to analyze the expression of CD44 adhesion molecule and its ligand osteopontin in papillary renal cell tumors, and to assess the possible prognostic significance of CD44 and osteopontin expression in papillary renal cell carcinomas. The expression of the standard and v6 exon containing isoforms of CD44 molecule, as well as of its ligand osteopontin, was immunohistochemically evaluated in 43 papillary renal cell tumors, which included 5 adenomas and 38 carcinomas. In order to assess their prognostic significance, the results obtained in papillary renal cell carcinomas were compared to usual clinicopathological parameters such as tumor size, histological grade, pathological stage, and Ki-67 proliferation index. Normal renal tissue was negative for CD44s and v6 isoforms, while the expression of osteopontin was found in distal tubular epithelial cells in the form of cytoplasmic granular positivity. CD44s and v6 isoforms were upregulated in 22 (58%) and 12 (32%) out of 38 carcinomas, respectively. Among all clinicopathological parameters examined, we only found significant association of CD44s-positive carcinomas with lower pathological stage (p=0.026). Papillary renal cell adenomas were generally negative for CD44s, except for focal positivity found in one sample. The osteopontin protein was detected in all adenomas and all papillary renal cell carcinomas, except one. Our results show constitutive expression of osteopontin in papillary renal tumors, including papillary renal cell adenomas. The upregulation of CD44s and v6 isoforms, although found in a considerable number of papillary renal cell carcinomas, does not appear to have any prognostic value in this type of renal cancer.