Basis for the acquisition of malignant potential by mouse cells cultivated in vitro.

Balb/c mouse embryo lines maintained in culture for over 200 generations under conditions that minimize cell-cell contact do not become tumorigenic. Lines cultivated under conditions where there is extensive cell contact become tumor-producing within 30 generations. The tissue-culture property that correlates best with tumorigenicity is the loss of contact inhibition of cell division.