Is renal cell (Grawitz) tumor a carcinosarcoma? Evidence from analysis of intermediate filament types

The expression of intermediate filament type was determined in 13 renal cell (Grawitz) tumors (10 primary renal tumors and 3 lymph node metastases). All of the tumors except one lymph node metastasis contained cells expressing vimentin intermediate filaments, generally a marker of mesodermally-derived tissues and their tumors, the sarcomas. In addition, the 10 primary renal tumors and two lymph node metastases contained cells expressing keratin proteins. Using a monoclonal antibody to keratins, specific for glandular epithelial cells, it has been shown that some of the tumor cells resemble adenocarcinomas, at least in this respect. Double immunofluorescence labeling demonstrated that some of the vimentin-containing cells contained keratin while others did not. Only occasional cells were found to contain keratin but not vimentin. However, one of the lymph node metastases was positive only for vimentin. Thus Grawitz tumor cells express intermediate filament types which are generally biological markers of both sarcomatous and carcinomatous tumors.