Ovarian clear cell carcinoma arising in a mucinous cystadenoma

Here we report a rare case of ovarian clear cell carcinoma (CC) arising in a mucinous cystadenoma. A 59-year-old woman presented with a dull pain at the left inguinal area. She was found to have a left ovarian cyst measuring 4.7 cm and underwent a salpingo-oophorectomy. The unilocular cyst contained thick mucin, lacking any solid components. Histopathologically, most of the cyst wall was lined with a single layer of tall columnar cells with basophilic mucin. Within limited areas, small glands consisting of clear cytoplasm aggregated and intermingled with or partially transitioned to the mucinous glands. The clear cell components had adenofibroma-like features devoid of significant nuclear atypia or stromal invasion, including distinctive foci of CC with a hobnail appearance and hyperchromatic nuclei surrounded by desmoplastic or hyalinized stroma. Immunohistochemically, both mucinous and clear cells were positive for estrogen receptor. Hepatocyte nuclear factor-1beta and laminin were positive in all of the clear cell components, in contrast to a consistent lack of staining in the mucinous epithelium. An eleven-month follow-up revealed no recurrence or metastasis. This case was considered as an early manifestation of ovarian CC arising in a mucinous cystadenoma in the absence of demonstrable endometriosis.