Ovarian clear cell carcinoma with an immature teratoma component showing ARID1A deficiency and an identical PIK3CA mutation.

We herein report a case of ovarian clear cell carcinoma with an immature teratoma component that exhibited aggressive behavior. A 47-year-old woman presented with abdominal distention, and computed tomography detected a cystic mass on the right ovary. The resected mass had mural nodules, most of which showed a pale-yellow appearance; some nodules had a heterogeneous cut surface with bright yellow and white areas. Histologically, the former nodules were composed of clear cell carcinoma, while the latter contained teratomatous tissues, such as immature skeletal muscle, adipose tissue, and enteric glands. The tumor was staged as pT1c. Despite adjuvant chemotherapy and additional lymph node dissection, she had local recurrence and multiple liver metastasis 6 months after the first surgery. The disease rapidly progressed, and she died 9 months after the first surgery. Clear cell carcinoma and immature teratoma both showed ARID1A deficiency and an identical PIK3CA mutation, which suggested their clonal relationship.