On the reversibility of tumor cells

A review is given of several cases in which a neoplastic cell becomes a normal one. Emphasis is placed on the Lucké adenocarcinoma in the frog and on the case of terminal differentiation. The mysteries of cell fusion studies are discussed as well as the experiments of Mintz et al on teratocarcinoma of the mouse. In the case of the Lucké adenocarcinoma, a cytoplasmic protein probably causes the reversal of the neoplastic state. In the case of terminal differentiation, both controls for the S and M period of the cell cycle are such that these events are shut off.