Ovarian clear-cell carcinoma, or clear-cell carcinoma of the ovary, also called ovarian clear-cell adenocarcinoma, is one of several subtypes of ovarian carcinoma – a subtype of epithelial ovarian cancer, in contrast to non-epithelial cancers. According to research, most ovarian cancers start at the epithelial layer which is the lining of the ovary. Within this epithelial group ovarian clear-cell carcinoma makes up 5–10%. It was recognized as a separate category of ovarian cancer by the World Health Organization in 1973. Its incidence rate differs across various ethnic groups. Reports from the United States show that the highest rates are among Asians with 11.1% versus whites with 4.8% and blacks at 3.1%. These numbers are consistent with the finding that although clear-cell carcinomas are rare in Western countries they are much more common in parts of Asia. Background There are two subtypes of ovarian carcinoma – epithelial and nonepithelial; ovarian clear-cell carcinoma is an epithelial ovarian cancer. The other major subtypes within this group include high-grade serous, endometrioid, mucinous, and low-grade serous. The serous type is the most common form of epithelial ovarian tumors. Cord-stromal and germ cell belong to the nonepithelial category which are much less common. Structure and function Ovarian clear-cell carcinoma often occurs as a pelvic mass that rarely appears bilaterally. The cells usually contain glycogen with large clear cytoplasm. It is also associated with endometriosis, a disorder of abnormal tissue growth outside of the uterus. The tumor cells emerge in a stepwise manner from adenofibromas which are benign endometriotic cysts. They also hold molecular genetic mutations in both ARID1A and PIK3CA, similar to other epithelial ovarian cancers. Mutations in ARID1A commonly contain phosphatase and tensin homolog (PTEN) that are hypothesized to contribute to clear-cell tumorigenesis. However, research also shows that inactivation of ARID1A alone does not lead to tumor initiation. However, clear-cell tumors rarely carry p53, BRCA1, or BRCA2 mutations. In addition, they also test negative for estrogen and progesterone receptors and Wilm tumor suppressor 1. Studies have also suggested that clear-cell carcinoma can occur with thromboembolic complications and hypercalcemia. Recurrence of tumor cells have been reported to involve lymph nodes and parenchymal organs. Research continues to look for ways to understand clear-cell tumor progression. A suggested mechanism is the amplification and overexpression of CCNE1 which is thought to promote the tumor's aggressive behavior. In addition, they also test negative for estrogen and progesterone receptors and Wilm tumor