Invasion of malignant cells in vivo and in vitro: similarities and differences

Progressive occupation of other tissues, accompanied by degeneration of these tissues indicates tumour invasiveness. Tumour cells presumed to be invading show alterations in shape, produce irregular cytoplasmic extensions, contain microfilament bundles and heterophagosomes. Confrontation of malignant cells with fragments of normal tissues in threedimensional culture produces pictures of invasion that would allow the pathologist to recognize that the tumour cells are malignant. Invasion of cells in these cultures correlates with formation of invasive tumours in syngeneic animals. Confrontation of malignant cells with non-malignant cells or tissues in twodimensional culture on artificial substrate mimics invasion less well. Twodimensional cultures might nevertheless present valuable complements to other models for the study of the activities of invasive cells. It is concluded that in vitro techniques deserve further interest from students of invasiveness because of their contribution to new insights into the mechanisms of invasions.