Malignant transformation of ovarian mature cystic teratoma with a predominant pulmonary type small cell carcinoma component.

A 68-year-old woman was diagnosed with mature cystic teratoma of the left ovary when she was 44 years old. The tumor recently enlarged rapidly, and abdominal magnetic resonance imaging revealed an intrapelvic cystic lesion, which measured 123 × 120 × 107 mm and contained a mural nodule. Under a clinical diagnosis of malignant transformation of mature cystic teratoma, bilateral salpingo-oophorectomy with total hysterectomy and omentectomy were performed. The resected specimen showed a unilocular cystic lesion containing a well-demarcated mural nodule measuring 35 × 30 × 25 mm in the left ovary. A microscopic examination revealed various types of carcinoma in the mural nodule: pulmonary type small cell carcinoma (65%), adenocarcinoma (25%), squamous cell carcinoma (5%), and transitional cell carcinoma (5%). Small cell carcinoma was positive for CD56, synaptophysin, and chromogranin A. The adenocarcinoma component showed intestinal phenotypes; i.e. cytokeratin (CK) 7(-), CK20(+), CDX2(+), estrogen receptor(-), and progesterone receptor (-). Interestingly, CDX2 positivity was retained in all of the carcinomas. It was assumed that the adenocarcinoma had arisen from an intestinal epithelium in the mature cystic teratoma and then differentiated into the diverse histological types mentioned above.