Cytological distinction between clear cell carcinoma and yolk sac tumor of the ovary.

Cytological characteristics of clear cell carcinoma (CCC) and yolk sac tumor (YST) of the ovary were examined and compared. Indices for differential diagnosis of these two histologically similar but biologically different tumors were analyzed based on cytological features of the tumor cells. The main results obtained were from three cases of CCC and one case of YST who underwent imprint smear or similar examinations. Seventeen cases of CCC and two of YST with positive cytology results, mainly obtained from ascites samples, were also examined. Cytological characteristics of CCC compared to those of YST were: more marked cohesiveness of tumor cells with less-marked pleomorphism, well-preserved cell borders, fine vesicular cytoplasm, evenly thickened nuclear membrane, and fewer nucleoli and multinucleated giant cells in number. Cells with large cytoplasmic vacuolation were infrequent, and hobnail-shaped tumor cells were rather few in number in CCC cases examined. On the other hand, in the case of YST, cells were more dyscohesive, with marked cellular pleomorphism, usually faint cell borders, no thickening of nuclear membrane and occasional presence of nuclear grooves. The "naked" cells were commonly observed. Further, nucleoli were frequently numerous in number, and multinucleated giant cells were frequently found which showed marked cellular and nuclear atypism. These characteristics found mainly in imprint smears were also relatively well preserved in specimens obtained from ascites or other metastatic sites. These findings indicate that detailed cytological examination can provide a means for differential diagnosis of CCC and YST, supplementing other clinical information.