Syncytial giant cell component. Review of 55 renal cell carcinomas.

Different types of multinucleated giant cells (MGC) have been documented in tumors with osteoclast-like appearance, with trophoblastic differentiation or as tumoral malignant giant cells. A new variety of MGC has been described in renal cell carcinoma. In order to study the frequency, nature and significance of this cellular type, we have reviewed our files. To assess the presence, nature and significance of these MGC in renal cell carcinomas and associated histologic subtype. To review all malignant renal tumors diagnosed in the last 5 years in our hospital and to carry out a morphologic and immunohistochemical study in renal cell carcinomas with syncytial type MGC. 55 renal cell carcinomas were reviewed. Clear cell (conventional) renal cell carcinoma was the most common type encountered (40 cases); two of these cases showed syncytial type MGC and low grade malignancy. Microscopically the MGC contained from 5 to 40 nuclei. Immunohistochemically, mononucleated and multinucleated cells were positive for cytokeratin CAM 5.2, cytokeratin AE1/AE3 and weakly positive for vimentin. Histiocytic, muscular, neural markers, beta-HCG and alpha-fetoprotein were negative. The presence of syncytial type MGC in renal cell carcinomas is an exceptional event. Among 55 renal cell carcinomas we found two cases, both of which were of clear cell subtype and low grade malignancy. The MGC proved positive for epithelial markers and probably are the result of mononucleated tumoral cell fusion. We are unaware of the impact of this MGC in the outcome of patients; such cells appear in low grade carcinomas and do not seem to be of dismal prognosis.