A COMPARATIVE IMMUNOHISTOCHEMICAL STUDY OF MALIGNANT MESOTHELIOMA ANDRENAL-CELL CARCINOMA - THE DIAGNOSTIC UTILITY OF LEU-M1, BER EP4, TAMM-HORSFALL PROTEIN AND THROMBOMODULIN

Metastatic renal cell carcinoma has occasionally been reported to mimi c malignant pleural mesothelioma. Morphologically, histochemically and immunohistochemically, similarities in the two tumours exist making t heir differentiation difficult, particularly in biopsy specimens. The aim of this study was to make a comparative immunohistochemical analys is of the two tumours by use of a panel of four antibodies (Leu M1; Be r EP4; thrombomodulin and Tamm-Horsfall protein). Their suitability in differentiating between the two tumours was assessed. We examined 20 cases of renal cell carcinoma and 20 cases of malignant pleural mesoth elioma. On immunostaining with Leu M1, 14 of 20 renal cell carcinomas were positive, yielding 70% sensitivity and 95% specificity and one of 20 mesotheliomas. In comparison, Ber EP4 antibody stained only seven of 20 of the renal cell carcinomas. In addition, it was noted that fou r tubulopapillary pattern renal cell carcinomas stained positively wit h both anti-Leu M1 antibody and Ber EP4 antibody. Thrombomodulin immun ostaining was present in 11 of 20 mesotheliomas (55% sensitivity and d emonstrated 95% specificity) and one of 20 renal cell carcinomas. For epithelial mesotheliomas only, thrombomodulin staining was identified in 10 of 14 cases. In the differentiation of renal cell carcinoma from epithelial mesothelioma we recommend the use of Leu M1 and thrombomod ulin as diagnostically useful markers. None of the antibodies used in this study was effective in distinguishing sarcomatoid renal cell carc inoma from sarcomatous mesothelioma. Tamm-Horsfall protein showed litt le diagnostic utility in differentiating the two tumours.