Expression of CD44 isoforms in human renal cell carcinomas.

A series of 27 renal cell carcinomas 4 oncocytomas and 7 samples of tumour free kidney parenchyma were analysed immunohistochemically using eight different CD44 isoform-specific monoclonal antibodies. In normal kidney expression of CD44 isoforms (containing variant exons v6, v7/8 and v10) was found predominantly at the distal tubules. The majority of clear cell carcinomas investigated showed expression of variant exons v5, v7/8 and v10, but not v6. Lack of CD44v6 expression was confirmed by reverse transcription-polymerase chain reaction analysis. Carcinomas of the chromophilic cell type were almost completely devoid of CD44 expression, including the standard form CD44s. This study shows that there are statistically significant differences in the CD44 expression pattern of the two major histological subtypes of renal cell carcinomas (clear cell and chromophilic carcinomas). Moreover, the almost complete lack of CD44 expression in chromophilic carcinomas contrasts with carcinomas of other histogenetic origin investigated including stomach, breast and lung which express various CD44 isoforms abundantly.