Tumors arising from injection of cultured murine placental cells into normal animals: direct evidence for placental origin of tumors of two histologic types.

Long-term culture of placentas obtained from the mating of a congenic C3H male mouse carrying a unique electrophoretic variant of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1) and a normal C3H female mouse has resulted in cell lines that have apparently undergone spontaneous malignant transformation in vitro. When injected into normal syngeneic animals, these cell lines have given rise to invasive carcinomas of two distinct histologic types, an adenocarcinoma and a poorly differentiated carcinoma. Both were demonstrated to be of placental origin by the continued presence of the allozyme coded on the paternal X-chromosome. Compared to murine tumors of other etiologies, these cell lines were characterized by a high intracellular alkaline phosphatase concentration.