The differentiation of carcinomas of teratomatous origin from embryonal carcinoma. A light and electron microscopic...

Carcinomas derived from teratomatous epithelium occur rarely in the metastases of patients with testicular cancer. These carcinomas of teratomatous origin (CTO) are easily confused with residual embryonal carcinoma (EC). For that reason, we compared the light and electron microscopic appearances of 6 CTOs with those of 12 ECs. As seen by light microscopy, the CTOs formed glands and more frequently had well-defined cytoplasmic borders, eosinophilic cytoplasm, and nonoverlapping, regular nuclei with small or absent nucleoli and little chromatin clumping and clearing, compared with the ECs. Mucin was present in the cells or glandular lumina of three CTOs but was absent in all the ECs. The demonstration of cytoplasmic glycogen was of no differential aid. The most useful differentiating ultrastructural features were long tight junctions and telolysosomes, which occurred in all of the EC but which were absent in the six cases of CTO. Desmosomes with inserting tonofilaments were present in three cases of CTO but were much less developed in EC. Two cases of CTO had microvilli with anchoring rootlets; such anchoring rootlets were not observed among EC. The distinction of CTO from residual EC is important, because CTO will likely need to be treated in a different manner.