Metastasis of small cell carcinoma of lung into an ovarian mucinous neoplasm: immunohistochemistry as a useful ancillary technique for diagnosis and classification of rare tumors.

The authors report the first case of ovarian mucinous adenocarcinoma with metastasis from a synchronous small cell neuroendocrine carcinoma of the lung. A 62-year-old white woman presented with weight loss and increased abdominal girth. She was found to have a large, complex cystic mass in the pelvis, and during the staging evaluation, a large, right pulmonary hilar mass was detected. Bronchial brushing as well as transbronchial fine-needle aspiration was diagnostic of small cell carcinoma. The patient received 3 cycles of chemotherapy with carboplatin and subsequently underwent a supracervical hysterectomy and bilateral salpingo-oophorectomy. A large, multiloculated cystic mass was found arising from the right ovary. Microscopic examination disclosed a mucinous neoplasm with both mucinous cystadenoma and mucinous papillary adenocarcinoma components. A microscopic focus of cells with "atypical" cytomorphologic features was detected within the mucinous neoplasm. Immunohistochemistry showed that group of cells to be positive for thyroid transcription factor 1 and chromogranin, confirming them to be metastasis from the pulmonary small cell neuroendocrine carcinoma. This case, in addition to being the first reported case of such metastasis, also highlights the diagnostic utility of immunohistochemistry as a reliable and very useful ancillary technique for the diagnosis of neoplasms with unusual clinical and/or histomorphologic presentations. The clinical and prognostic implications are also discussed.