CLEAR CELL CARCINOMA OF THE OVARY. This is the most commonly missed pattern of clear cells carcinoma in the ovary. Another pattern that is commonly missed is the papillary pattern which resembles a borderline serous tumor. Most often the luminal contents are watery, but can be thick and tenacious. The tumor is difficult to recognize because the atypia is not pronounced. Closer examination will reveal hobnailed cells (image 2). Smaller cysts often reveal the diagnostic clear cells. Tumor cells are characteristically WT1, ER, PR negative which distinguishes it from a serous tumor. However, this immunoprofile is also true of mucinous tumors of the ovary, although that is uncommonly in the differential. Tumor cells are positive for Napsin, HNF1beta and Arid IA, which distinguishes it from its mimics.
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