Malignant neoplasms of differentiated cells occurring after retinoic acid treatment of murine embryonal carcinomas in vivo.

Murine embryonal carcinoma tumors were induced to differentiate in vivo using retinoic acid. Six mice bearing seven tumors survived more than 100 days after treatment. Histological samples of these tumors showed no residual embryonal carcinoma cells, and, for the most part, they were benign cystic teratomas. Three tumors, in addition to the benign tissue, had solid, mitotically active areas. Two of these tumors upon transplantation gave rise to progressively growing, potentially lethal tumors which have proven to be permanently transplantable cell lines. Using techniques of light and electron microscopy, immunohistochemistry, flow microfluorometry, and cytogenetics, we have characterized these lines. One is a chondrosarcoma, and one is a glioma:chondrosarcoma mixture. Both are chromosomally different from the parent embryonal carcinoma stem cell line, but both were clearly derived from it.