Diagnosis of metastatic renal cell and thyroid carcinomas by intermediate filament typing and cytology of tumor cells in fine needle aspirates.

Coexpression of keratin and vimentin was found in carcinoma cells of 13 fine needle aspirates of metastatic lesions that showed some cytologic features considered to be consistent with a renal or thyroid origin, but in which a large number of other possible primary sites would have to be taken into account on the basis of the morphologic evidence alone. Immunochemistry thus narrowed the cytologic differential diagnosis to thyroid, renal, endometrial and ovarian carcinomas, which are known to show true coexpression of keratin and vimentin. In most cases, clinical data available at the time of the fine needle aspiration supported the thyroid or renal origin of the carcinoma cells found in the aspirates. In two cases, which lacked significant clinical information, the diagnosis of metastatic renal cell carcinoma was provided on the basis of the combined morphologic and immunocytochemical evidence. In these two cases, computed tomography or ultrasonography revealed kidney tumors, which were removed and confirmed histologically to be clear cell carcinomas.