Carcinomas of ovary and lung with clear cell features: Can immunohistochemistry help in differential diagnosis?

Metastatic lung carcinomas with clear cell morphology can be confused with primary ovarian clear cell carcinomas. We performed immunohistochemical stains in 14 cases of non-small cell lung carcinomas with clear cell features and 14 cases of ovarian clear cell carcinomas using a panel of markers, including thyroid transcription factor 1 (TTF-1), carcinoembryonic antigen (CEA), Wilms tumor gene 1, octamer-binding transcription factor 4 (OCT-4), cancer antigen 125 (CA-125), estrogen receptor, and progesterone receptor. Among non-small cell lung carcinomas with clear cell features, 87.5% of adenocarcinomas (or 50% overall frequency in lung carcinomas) were positive for TTF-1, whereas none of the ovarian clear cell carcinomas were positive (P = 0.002). All 14 ovarian clear cell carcinomas stained for CA-125 as compared with 1 non-small cell lung carcinoma (P < 0.001). On the other hand, 85% of non-small cell lung carcinomas stained for CEA, whereas none of the ovarian clear cell carcinomas did (P < 0.001). Interestingly, 4 ovarian clear cell carcinomas (28%) showed positive staining for the germ cell marker OCT-4. Either lung or ovarian carcinomas stained for Wilms tumor gene 1, estrogen receptor, or progesterone receptor very infrequently; and the difference between the 2 groups was not statistically significant. Our results suggest that an immunohistochemical panel consisting of TTF-1, CEA, CA-125, and OCT-4 is helpful in distinguishing most pulmonary and ovarian carcinomas with clear cell features.